diff --git a/Network/Wai/Logger/Prefork.hs b/Network/Wai/Logger/Prefork.hs
--- a/Network/Wai/Logger/Prefork.hs
+++ b/Network/Wai/Logger/Prefork.hs
@@ -2,9 +2,10 @@
     logCheck
   , logInit
   , logController
+  , LogController
   , LogType(..)
   , FileLogSpec(..)
-  , LogController
+  , LogFlusher
   ) where
 
 import Control.Concurrent
@@ -14,25 +15,37 @@
 import Network.Wai.Logger.Prefork.Types
 import System.Log.FastLogger
 
+-- |
+-- Checking if a log file can be written if 'LogType' is 'LogFile'.
 logCheck :: LogType -> IO ()
-logCheck LogNone   = return ()
-logCheck LogStdout = return ()
-logCheck (LogFile spec) = check spec
+logCheck LogNone          = return ()
+logCheck LogStdout        = return ()
+logCheck (LogFile spec _) = check spec
 
-logInit :: IPAddrSource -> LogType -> IO ApacheLogger
-logInit _ LogNone            = noLoggerInit
-logInit ipsrc LogStdout      = stdoutApacheLoggerInit ipsrc True
-logInit ipsrc (LogFile spec) = fileLoggerInit ipsrc spec
+-- |
+-- Creating 'ApacheLogger' according to 'LogType'.
+logInit :: IPAddrSource -> LogType -> IO (ApacheLogger, LogFlusher)
+logInit _     LogNone               = noLoggerInit
+logInit ipsrc LogStdout             = stdoutLoggerInit ipsrc
+logInit ipsrc (LogFile spec signal) = fileLoggerInit ipsrc spec signal
 
-noLoggerInit :: IO ApacheLogger
-noLoggerInit = return noLogger
+noLoggerInit :: IO (ApacheLogger, LogFlusher)
+noLoggerInit = return (noLogger, noFlusher)
   where
     noLogger _ _ _ = return ()
+    noFlusher = return ()
 
+stdoutLoggerInit :: IPAddrSource -> IO (ApacheLogger, LogFlusher)
+stdoutLoggerInit ipsrc = do
+    lgr <- stdoutApacheLoggerInit ipsrc True
+    return (lgr, return ())
+
+-- |
+-- Creating a log controller against child processes.
 logController :: LogType -> LogController
-logController LogNone        = noLoggerController
-logController LogStdout      = noLoggerController
-logController (LogFile spec) = fileLoggerController spec
+logController LogNone               = noLoggerController
+logController LogStdout             = noLoggerController
+logController (LogFile spec signal) = fileLoggerController spec signal
 
 noLoggerController :: LogController
-noLoggerController _ = forever $ threadDelay 10000000
+noLoggerController _ = forever $ threadDelay maxBound
diff --git a/Network/Wai/Logger/Prefork/File.hs b/Network/Wai/Logger/Prefork/File.hs
--- a/Network/Wai/Logger/Prefork/File.hs
+++ b/Network/Wai/Logger/Prefork/File.hs
@@ -20,25 +20,22 @@
 getLogger (LoggerRef ref) = readIORef ref
 
 setLogger :: LoggerRef -> Logger -> IO ()
-setLogger (LoggerRef ref) logger = writeIORef ref logger
+setLogger (LoggerRef ref) = writeIORef ref
 
 ----------------------------------------------------------------
 
-fileLoggerInit :: IPAddrSource -> FileLogSpec -> IO ApacheLogger
-fileLoggerInit ipsrc spec = do
+type LogFlusher = IO ()
+
+fileLoggerInit :: IPAddrSource -> FileLogSpec -> Signal
+               -> IO (ApacheLogger, LogFlusher)
+fileLoggerInit ipsrc spec signal = do
     hdl <- open spec
     logger <- mkLogger False hdl
     logref <- LoggerRef <$> newIORef logger
-    _ <- forkIO $ fileFlusher logref
-    _ <- installHandler sigUSR1 (Catch $ reopen spec logref) Nothing
-    return $ fileLogger ipsrc logref
+    void . forkIO $ fileFlusher logref
+    void $ installHandler signal (Catch $ reopen spec logref) Nothing
+    return (fileLogger ipsrc logref, fileFlusher' logref)
 
-{-
- 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 = openFile (log_file spec) AppendMode
 
@@ -59,12 +56,15 @@
 fileFlusher :: LoggerRef -> IO ()
 fileFlusher logref = forever $ do
     threadDelay 10000000
-    getLogger logref >>= loggerFlush
+    fileFlusher' logref
 
+fileFlusher' :: LoggerRef -> IO ()
+fileFlusher' logref = getLogger logref >>= loggerFlush
+
 ----------------------------------------------------------------
 
-fileLoggerController :: FileLogSpec -> LogController
-fileLoggerController spec pids = forever $ do
+fileLoggerController :: FileLogSpec -> Signal -> LogController
+fileLoggerController spec signal pids = forever $ do
     isOver <- over
     when isOver $ do
         rotate spec
@@ -78,7 +78,7 @@
             return True
           else
             return False
-    sendSignal pid = signalProcess sigUSR1 pid `catch` ignore
+    sendSignal pid = signalProcess signal pid `catch` ignore
     handler :: SomeException -> IO Bool
     handler _ = return False
     ignore :: SomeException -> IO ()
diff --git a/Network/Wai/Logger/Prefork/Types.hs b/Network/Wai/Logger/Prefork/Types.hs
--- a/Network/Wai/Logger/Prefork/Types.hs
+++ b/Network/Wai/Logger/Prefork/Types.hs
@@ -5,8 +5,11 @@
   ) where
 
 import System.Log.FastLogger
-import System.Posix (ProcessID)
+import System.Posix (ProcessID, Signal)
 
-data LogType = LogNone | LogStdout | LogFile FileLogSpec
+data LogType = LogNone
+             | LogStdout
+               -- | 'Signal' is used to tell child processes to reopen a log file.
+             | LogFile FileLogSpec Signal
 
 type LogController = [ProcessID] -> IO ()
diff --git a/wai-logger-prefork.cabal b/wai-logger-prefork.cabal
--- a/wai-logger-prefork.cabal
+++ b/wai-logger-prefork.cabal
@@ -1,5 +1,5 @@
 Name:                   wai-logger-prefork
-Version:                0.2.0
+Version:                0.2.1
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3