diff --git a/bytable.cabal b/bytable.cabal
--- a/bytable.cabal
+++ b/bytable.cabal
@@ -2,7 +2,7 @@
 build-type:	Simple
 
 name:		bytable
-version:	0.0.0.3
+version:	0.0.0.4
 stability:	Experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
@@ -28,7 +28,7 @@
 source-repository	this
     type:	git
     location:	git://github.com/YoshikuniJujo/forest
-    tag:	bytable-0.0.0.3
+    tag:	bytable-0.0.0.4
 
 library
     hs-source-dirs:	src
diff --git a/src/Codec/Bytable/BigEndian.hs b/src/Codec/Bytable/BigEndian.hs
--- a/src/Codec/Bytable/BigEndian.hs
+++ b/src/Codec/Bytable/BigEndian.hs
@@ -12,7 +12,7 @@
 		| BS.length bs <= 4 = Right $ byteStringToNum bs
 		| otherwise = Left
 			"Codec.Bytable.BigEndian: Bytable Int: too large"
-	toByteString = integralToByteString
+	toByteString = integralToByteStringN 4
 
 instance Bytable Integer where
 	fromByteString bs = Right $ byteStringToNum bs
@@ -23,14 +23,14 @@
 		| BS.length bs <= 2 = Right $ byteStringToNum bs
 		| otherwise = Left
 			"Codec.Bytable.BigEndian: Bytable Word16: too large"
-	toByteString = integralToByteString
+	toByteString = integralToByteStringN 2
 
 instance Bytable Word32 where
 	fromByteString bs
 		| BS.length bs <= 4 = Right $ byteStringToNum bs
 		| otherwise = Left
 			"Codec.Bytable.BigEndian: Bytable Word32: too large"
-	toByteString = integralToByteString
+	toByteString = integralToByteStringN 4
 
 byteStringToNum :: (Num n, Bits n) => BS.ByteString -> n
 byteStringToNum = wordsToNum . reverse . BS.unpack
@@ -41,6 +41,11 @@
 
 integralToByteString :: (Integral n, Bits n) => n -> BS.ByteString
 integralToByteString = BS.pack . reverse . integralToWords
+
+integralToByteStringN :: (Integral n, Bits n) => Int -> n -> BS.ByteString
+integralToByteStringN n = BS.pack .
+	(\ws -> replicate (n - length ws) 0 ++ ws) .
+	reverse . integralToWords
 
 integralToWords :: (Integral n, Bits n) => n -> [Word8]
 integralToWords 0 = []