diff --git a/Network/Wai/Logger.hs b/Network/Wai/Logger.hs
--- a/Network/Wai/Logger.hs
+++ b/Network/Wai/Logger.hs
@@ -6,6 +6,7 @@
 --
 -- > {-# LANGUAGE OverloadedStrings #-}
 -- > module Main where
+-- >
 -- > import Blaze.ByteString.Builder (fromByteString)
 -- > import Control.Monad.IO.Class (liftIO)
 -- > import Data.ByteString.Char8
@@ -14,6 +15,7 @@
 -- > import Network.Wai.Handler.Warp
 -- > import Network.Wai.Logger
 -- > import System.IO
+-- > import System.Log.FastLogger
 -- >
 -- > main :: IO ()
 -- > main = do
@@ -25,27 +27,20 @@
 -- >     date <- liftIO $ getDate dref
 -- >     let status = status200
 -- >         len = 4
--- >     liftIO $ hPutLogStr stdout $ apacheFormat date req status (Just len)
+-- >     liftIO $ hPutLogStr stdout $ apacheFormat FromSocket date req status (Just len)
 -- >     liftIO $ hFlush stdout
 -- >     return $ ResponseBuilder status
--- >                              [("Content-Type", "text/plain")
--- >                              ,("Content-Length", pack (show len))]
--- >            $ fromByteString "PONG"
+-- >         [("Content-Type", "text/plain")
+-- >         ,("Content-Length", pack (show len))]
+-- >         $ fromByteString "PONG"
 
 module Network.Wai.Logger (
-  -- * Low level modules
-    module Network.Wai.Logger.Date
-  , module Network.Wai.Logger.File
-  , module Network.Wai.Logger.Format
+    module Network.Wai.Logger.Format
+  , module Network.Wai.Logger.Date
   , module Network.Wai.Logger.Utils
-  , module Network.Wai.Logger.IO
-  -- * High level modules
-  -- | See "Network.Wai.Logger.Prefork".
   ) where
 
 import Network.Wai.Logger.Date
-import Network.Wai.Logger.File
 import Network.Wai.Logger.Format
-import Network.Wai.Logger.IO
 import Network.Wai.Logger.Utils
 
diff --git a/Network/Wai/Logger/File.hs b/Network/Wai/Logger/File.hs
deleted file mode 100644
--- a/Network/Wai/Logger/File.hs
+++ /dev/null
@@ -1,42 +0,0 @@
-module Network.Wai.Logger.File where
-
-import Control.Monad
-import System.Directory
-import System.FilePath
-
--- | The spec for logging files
-data FileLogSpec = FileLogSpec {
-    log_file :: String
-  , log_file_size :: Integer
-  , log_backup_number :: Int
-  }
-
--- | Checking if a log file can be written.
-check :: FileLogSpec -> IO ()
-check spec = do
-    dirExist <- doesDirectoryExist dir
-    unless dirExist $ fail $ dir ++ " does not exist or is not a directory."
-    dirPerm <- getPermissions dir
-    unless (writable dirPerm) $ fail $ dir ++ " is not writable."
-    exist <- doesFileExist file
-    when exist $ do
-        perm <- getPermissions file
-        unless (writable perm) $ fail $ file ++ " is not writable."
-  where
-    file = log_file spec
-    dir = takeDirectory file
-
--- | Rotating log files.
-rotate :: FileLogSpec -> IO ()
-rotate spec = mapM_ move srcdsts
-  where
-    path = log_file spec
-    n = log_backup_number spec
-    dsts' = reverse . ("":) . map (('.':). show) $ [0..n-1]
-    dsts = map (path++) dsts'
-    srcs = tail dsts
-    srcdsts = zip srcs dsts
-    move (src,dst) = do
-        exist <- doesFileExist src
-        when exist $ renameFile src dst
-
diff --git a/Network/Wai/Logger/Format.hs b/Network/Wai/Logger/Format.hs
--- a/Network/Wai/Logger/Format.hs
+++ b/Network/Wai/Logger/Format.hs
@@ -11,13 +11,14 @@
 import Blaze.ByteString.Builder.Char8
 import Data.ByteString.Char8 ()
 import Data.CaseInsensitive
+import Data.List
 import Data.Maybe
 import Data.Monoid
 import Network.HTTP.Types
 import Network.Wai
 import Network.Wai.Logger.Date
-import Network.Wai.Logger.IO
 import Network.Wai.Logger.Utils
+import System.Log.FastLogger
 
 {-| Source from which the IP source address of the client is obtained.
 -}
@@ -82,17 +83,16 @@
 lookupRequestField' k req = fromMaybe "" . lookup k $ requestHeaders req
 
 getSourceIP :: IPAddrSource -> Request -> LogStr
-getSourceIP FromSocket req = LS $ showSockAddr (remoteHost req)
-getSourceIP FromHeader req = LB addr
-  where
-    maddr = lookup "x-real-ip" hdrs >> lookup "x-forwarded-for" hdrs
-    addr = fromMaybe "" maddr
-    hdrs = requestHeaders req
+getSourceIP FromSocket = LS . showSockAddr . remoteHost
+getSourceIP FromHeader = LB . getSource
 
 getSourceIP' :: IPAddrSource -> Request -> Builder
-getSourceIP' FromSocket req = fromString . showSockAddr . remoteHost $ req
-getSourceIP' FromHeader req = fromByteString addr
+getSourceIP' FromSocket = fromString . showSockAddr . remoteHost
+getSourceIP' FromHeader = fromByteString . getSource
+
+getSource :: Request -> Ascii
+getSource req = addr
   where
-    maddr = lookup "x-real-ip" hdrs >> lookup "x-forwarded-for" hdrs
-    addr = fromMaybe "" maddr
+    maddr = find (\x -> fst x `elem` ["x-real-ip", "x-forwarded-for"]) hdrs
+    addr = maybe "" snd maddr
     hdrs = requestHeaders req
diff --git a/Network/Wai/Logger/IO.hs b/Network/Wai/Logger/IO.hs
deleted file mode 100644
--- a/Network/Wai/Logger/IO.hs
+++ /dev/null
@@ -1,94 +0,0 @@
-{-# LANGUAGE DoAndIfThenElse, BangPatterns #-}
-{-# LANGUAGE NoImplicitPrelude, RecordWildCards #-}
-
-module Network.Wai.Logger.IO (
-    LogStr(..)
-  , hPutLogStr
-  -- * Builder
-  , initHandle, hPutBuilder
-  ) where
-
-import Blaze.ByteString.Builder
-import qualified Data.ByteString as BS
-import Data.ByteString.Internal (ByteString(..), c2w)
-import Data.List
-import Data.Maybe
-import Foreign
-import GHC.Base
-import GHC.IO.Buffer
-import qualified GHC.IO.BufferedIO as Buffered
-import GHC.IO.Handle.Internals
-import GHC.IO.Handle.Text
-import GHC.IO.Handle.Types
-import GHC.IORef
-import GHC.Num
-import GHC.Real
-import System.IO
-
-{-| A date type to contain 'String' and 'ByteString'.
-    This data is exported so that format can be defined.
-    This would be replaced with 'Builder' someday.
--}
-data LogStr = LS !String | LB !ByteString
-
-{-| The 'hPut' function to copy a list of 'LogStr' to the buffer
-    of 'Handle' directly.
-    If 'Handle' is associated with a file, 'AppendMode' must be used.
--}
-hPutLogStr :: Handle -> [LogStr] -> IO ()
-hPutLogStr handle bss =
-  wantWritableHandle "hPutLogStr" handle $ \h_ -> bufsWrite h_ bss
-
-bufsWrite :: Handle__-> [LogStr] -> IO ()
-bufsWrite h_@Handle__{..} bss = do
-    old_buf@Buffer{
-        bufRaw = old_raw
-      , bufR = w
-      , bufSize = size
-      } <- readIORef haByteBuffer
-    if size - w > len then do
-        withRawBuffer old_raw $ \ptr ->
-            go (ptr `plusPtr` w)  bss
-        writeIORef haByteBuffer old_buf{ bufR = w + len }
-    else do
-        old_buf' <- Buffered.flushWriteBuffer haDevice old_buf
-        writeIORef haByteBuffer old_buf'
-        bufsWrite h_ bss
-  where
-    len = foldl' (\x y -> x + getLength y) 0 bss
-    getLength (LB s) = BS.length s
-    getLength (LS s) = length s
-    go :: Ptr Word8 -> [LogStr] -> IO ()
-    go _ [] = return ()
-    go dst (LB b:bs) = do
-      dst' <- copy dst b
-      go dst' bs
-    go dst (LS s:ss) = do
-      dst' <- copy' dst s
-      go dst' ss
-
-copy :: Ptr Word8 -> ByteString -> IO (Ptr Word8)
-copy dst (PS ptr off len) = withForeignPtr ptr $ \s -> do
-    let src = s `plusPtr` off
-    memcpy dst src (fromIntegral len)
-    return (dst `plusPtr` len)
-
-copy' :: Ptr Word8 -> String -> IO (Ptr Word8)
-copy' dst [] = return dst
-copy' dst (x:xs) = do
-    poke dst (c2w x)
-    copy' (dst `plusPtr` 1) xs
-
-{-| Setting a proper buffering to 'Handle'.
--}
-initHandle :: Handle -> IO ()
-initHandle hdl = hSetBuffering hdl (BlockBuffering (Just 4096))
-
-{-| The 'hPut' function directory to copy 'Builder' to the buffer.
-    If 'Handle' is associated with a file, 'AppendMode' must be used.
-    The current implementation is inefficient at this moment.
-    'initHandle' must be called once beforehand if this function is used.
-    This would replace 'hPutLogStr' someday.
--}
-hPutBuilder :: Handle -> Builder -> IO ()
-hPutBuilder hdl = BS.hPut hdl . toByteString
diff --git a/Network/Wai/Logger/Prefork.hs b/Network/Wai/Logger/Prefork.hs
deleted file mode 100644
--- a/Network/Wai/Logger/Prefork.hs
+++ /dev/null
@@ -1,41 +0,0 @@
-module Network.Wai.Logger.Prefork (
-    logCheck
-  , logInit
-  , logController
-  , ApacheLogger
-  , LogType(..)
-  , IPAddrSource(..)
-  , FileLogSpec(..)
-  , LogController
-  ) where
-
-import Control.Concurrent
-import Control.Monad
-import Network.Wai.Logger.File
-import Network.Wai.Logger.Format
-import Network.Wai.Logger.Prefork.File
-import Network.Wai.Logger.Prefork.Stdout
-import Network.Wai.Logger.Prefork.Types
-
-logCheck :: LogType -> IO ()
-logCheck LogNone   = return ()
-logCheck LogStdout = return ()
-logCheck (LogFile spec) = check spec
-
-logInit :: IPAddrSource -> LogType -> IO ApacheLogger
-logInit _ LogNone            = noLoggerInit
-logInit ipsrc LogStdout      = stdoutLoggerInit ipsrc
-logInit ipsrc (LogFile spec) = fileLoggerInit ipsrc spec
-
-noLoggerInit :: IO ApacheLogger
-noLoggerInit = return noLogger
-  where
-    noLogger _ _ _ = return ()
-
-logController :: LogType -> LogController
-logController LogNone        = noLoggerController
-logController LogStdout      = noLoggerController
-logController (LogFile spec) = fileLoggerController spec
-
-noLoggerController :: LogController
-noLoggerController _ = forever $ threadDelay 10000000
diff --git a/Network/Wai/Logger/Prefork/File.hs b/Network/Wai/Logger/Prefork/File.hs
deleted file mode 100644
--- a/Network/Wai/Logger/Prefork/File.hs
+++ /dev/null
@@ -1,96 +0,0 @@
-{-# LANGUAGE DoAndIfThenElse #-}
-
-module Network.Wai.Logger.Prefork.File where
-
-import Control.Applicative
-import Control.Concurrent
-import Control.Exception (handle, SomeException, catch)
-import Control.Monad
-import Data.IORef
-import Network.Wai.Logger.Date
-import Network.Wai.Logger.File
-import Network.Wai.Logger.Format
-import Network.Wai.Logger.IO
-import Network.Wai.Logger.Prefork.Types
-import Prelude hiding (catch)
-import System.IO
-import System.Posix
-
-----------------------------------------------------------------
-
-logBufSize :: Int
-logBufSize = 4096
-
-----------------------------------------------------------------
-
-newtype HandleRef = HandleRef (IORef Handle)
-
-getHandle :: HandleRef -> IO Handle
-getHandle (HandleRef ref) = readIORef ref
-
-----------------------------------------------------------------
-
-fileLoggerInit :: IPAddrSource -> FileLogSpec -> IO ApacheLogger
-fileLoggerInit ipsrc spec = do
-    hdl <- open spec
-    hdlref <- HandleRef <$> newIORef hdl
-    forkIO $ fileFlusher hdlref
-    dateref <- dateInit
-    installHandler sigUSR1 (Catch $ reopen spec hdlref) Nothing
-    return $ fileLogger ipsrc dateref hdlref
-
-{-
- For BlockBuffering, hPut flushes the buffer before writing
- the target string. In other words, hPut does not split
- the target string. So, to implment multiple line buffering,
- just use BlockBuffering.
--}
-open :: FileLogSpec -> IO Handle
-open spec = do
-    hdl <- openFile file AppendMode
-    hSetBuffering hdl (BlockBuffering (Just logBufSize))
-    return hdl
-  where
-    file = log_file spec
-
-reopen :: FileLogSpec -> HandleRef -> IO ()
-reopen spec (HandleRef ref) = do
-    hdl <- open spec
-    oldhdl <- atomicModifyIORef ref (\oh -> (hdl,oh))
-    hClose oldhdl
-
-----------------------------------------------------------------
-
-fileLogger :: IPAddrSource -> DateRef -> HandleRef -> ApacheLogger
-fileLogger ipsrc dateref hdlref req status msiz = do
-    date <- getDate dateref
-    hdl <- getHandle hdlref
-    hPutLogStr hdl $ apacheFormat ipsrc date req status msiz
-
-fileFlusher :: HandleRef -> IO ()
-fileFlusher hdlref = forever $ do
-    threadDelay 10000000
-    getHandle hdlref >>= hFlush
-
-----------------------------------------------------------------
-
-fileLoggerController :: FileLogSpec -> LogController
-fileLoggerController spec pids = forever $ do
-    isOver <- over
-    when isOver $ do
-        rotate spec
-        mapM_ sendSignal pids
-    threadDelay 10000000
-  where
-    file = log_file spec
-    over = handle handler $ do
-        siz <- fromIntegral . fileSize <$> getFileStatus file
-        if siz > log_file_size spec then
-            return True
-        else
-            return False
-    sendSignal pid = signalProcess sigUSR1 pid `catch` ignore
-    handler :: SomeException -> IO Bool
-    handler _ = return False
-    ignore :: SomeException -> IO ()
-    ignore _ = return ()
diff --git a/Network/Wai/Logger/Prefork/Stdout.hs b/Network/Wai/Logger/Prefork/Stdout.hs
deleted file mode 100644
--- a/Network/Wai/Logger/Prefork/Stdout.hs
+++ /dev/null
@@ -1,22 +0,0 @@
-module Network.Wai.Logger.Prefork.Stdout (stdoutLoggerInit) where
-
-import Control.Applicative
-import Data.ByteString.Char8 (pack)
-import Network.Wai.Logger.Date
-import Network.Wai.Logger.Format
-import Network.Wai.Logger.IO
-import Network.Wai.Logger.Prefork.Types
-import qualified Data.ByteString as BS
-
-stdoutLoggerInit :: IPAddrSource -> IO ApacheLogger
-stdoutLoggerInit ipsrc = stdoutLogger ipsrc <$> dateInit
-
-stdoutLogger :: IPAddrSource -> DateRef -> ApacheLogger
-stdoutLogger ipsrc dateref req status msiz = do
-    date <- getDate dateref
-    putToStdout $ logmsg date
-  where
-    putToStdout = BS.putStr . BS.concat . map toBS
-    logmsg date = apacheFormat ipsrc date req status msiz
-    toBS (LS s) = pack s
-    toBS (LB s) = s
diff --git a/Network/Wai/Logger/Prefork/Types.hs b/Network/Wai/Logger/Prefork/Types.hs
deleted file mode 100644
--- a/Network/Wai/Logger/Prefork/Types.hs
+++ /dev/null
@@ -1,17 +0,0 @@
-module Network.Wai.Logger.Prefork.Types (
-    ApacheLogger
-  , FileLogSpec(..)
-  , LogType(..)
-  , LogController
-  ) where
-
-import Network.HTTP.Types
-import Network.Wai
-import Network.Wai.Logger.File
-import System.Posix (ProcessID)
-
-data LogType = LogNone | LogStdout | LogFile FileLogSpec
-
-type ApacheLogger = Request -> Status -> Maybe Integer -> IO ()
-
-type LogController = [ProcessID] -> IO ()
diff --git a/wai-logger.cabal b/wai-logger.cabal
--- a/wai-logger.cabal
+++ b/wai-logger.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-logger
-Version:                0.0.2
+Version:                0.1.0
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -13,19 +13,12 @@
   GHC-Options:          -Wall -fno-warn-unused-do-bind
   Exposed-Modules:      Network.Wai.Logger
                         Network.Wai.Logger.Date
-                        Network.Wai.Logger.File
                         Network.Wai.Logger.Format
-                        Network.Wai.Logger.IO
                         Network.Wai.Logger.Utils
-                        Network.Wai.Logger.Prefork
-  Other-Modules:        Network.Wai.Logger.Prefork.File
-                        Network.Wai.Logger.Prefork.Stdout
-                        Network.Wai.Logger.Prefork.Types
-  Build-Depends:        base >= 4 && < 5, wai,
-                        http-types, bytestring, filepath,
-                        directory, old-locale, case-insensitive,
-                        time, deepseq, unix, byteorder, network,
-                        blaze-builder
+  Build-Depends:        base >= 4 && < 5, time, old-locale,
+                        unix, bytestring, blaze-builder,
+                        wai, fast-logger, http-types, case-insensitive,
+                        network, byteorder
 Source-Repository head
   Type:                 git
   Location:             git://github.com/kazu-yamamoto/wai-logger.git