diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+# 0.17.2
+* send 302 if file not midified.
+
 # 0.17.1
 * relax switchQuery.
 
diff --git a/apiary.cabal b/apiary.cabal
--- a/apiary.cabal
+++ b/apiary.cabal
@@ -1,5 +1,5 @@
 name:                apiary
-version:             0.17.1
+version:             0.17.2
 synopsis:            Simple and type safe web framework that can be automatically generate API documentation.
 description:
   Simple and type safe web framework that can be automatically generate API documentation.
@@ -116,6 +116,8 @@
                      , hashable             >=1.1   && <1.3
                      , time                 >=1.4   && <1.6
                      , process              >=1.2   && <1.3
+                     , unix-compat          >=0.4   && <0.5
+                     , http-date            >=0.0   && <0.1
 
   if impl(ghc < 7.8)
     build-depends:     tagged               >=0.7   && <0.8
diff --git a/src/Control/Monad/Apiary/Action/Internal.hs b/src/Control/Monad/Apiary/Action/Internal.hs
--- a/src/Control/Monad/Apiary/Action/Internal.hs
+++ b/src/Control/Monad/Apiary/Action/Internal.hs
@@ -16,6 +16,8 @@
 
 module Control.Monad.Apiary.Action.Internal where
 
+import System.PosixCompat.Files
+
 import Control.Applicative
 import Control.Monad
 import Control.Monad.Trans
@@ -25,6 +27,7 @@
 import Control.Monad.Trans.Control
 
 import Network.Mime hiding (Extension)
+import Network.HTTP.Date
 import Network.HTTP.Types
 import Network.Wai
 import qualified Network.Wai.Parse as P
@@ -426,15 +429,26 @@
 reset = modifyState (\s -> s { actionResponse = mempty } )
 
 -- | set response body file content, without set Content-Type. since 0.1.0.0.
-file' :: Monad m => FilePath -> Maybe FilePart -> ActionT exts m ()
+file' :: MonadIO m => FilePath -> Maybe FilePart -> ActionT exts m ()
 file' f p = modifyState (\s -> s { actionResponse = ResponseFile f p } )
 
 -- | set response body file content and detect Content-Type by extension. since 0.1.0.0.
-file :: Monad m => FilePath -> Maybe FilePart -> ActionT exts m ()
+--
+-- file modification check since 0.17.2.
+file :: MonadIO m => FilePath -> Maybe FilePart -> ActionT exts m ()
 file f p = do
-    mime <- mimeType <$> getConfig
-    contentType (mime f)
-    file' f p
+    mbims <- (>>= parseHTTPDate) . lookup "If-Modified-Since" <$> getHeaders
+    e <- liftIO $ fileExist f
+    t <- if e
+         then liftIO $ Just . epochTimeToHTTPDate . modificationTime <$> getFileStatus f
+         else return Nothing
+    case mbims of
+        Just ims | maybe False (ims >=) t -> reset >> status status304 >> stop
+        _ -> do
+            mime <- mimeType <$> getConfig
+            contentType (mime f)
+            maybe (return ()) (addHeader "Last-Modified" . formatHTTPDate) t
+            file' f p
 
 -- | append response body from builder. since 0.1.0.0.
 builder :: Monad m => Builder -> ActionT exts m ()