diff --git a/src/Data/ByteString/Lazy/ToolsYj.hs b/src/Data/ByteString/Lazy/ToolsYj.hs
--- a/src/Data/ByteString/Lazy/ToolsYj.hs
+++ b/src/Data/ByteString/Lazy/ToolsYj.hs
@@ -1,11 +1,57 @@
 {-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables, TypeApplications #-}
 {-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
 
 module Data.ByteString.Lazy.ToolsYj (
-	splitAt' ) where
 
+	-- * FROM/TO BITS
+
+	fromBits, fromBits', toBits, toBits',
+
+	-- * FROM/TO BITS -- BIG ENDIEN
+
+	fromBitsBE', toBitsBE,
+
+	-- * SPLIT AT
+
+	splitAt'
+
+	) where
+
+import Data.Bits
+import Data.Bits.ToolsYj
+import Data.Bool
 import Data.Int
 import Data.ByteString.Lazy qualified as LBS
+
+fromBits :: Bits b => b -> LBS.ByteString
+fromBits = LBS.unfoldr \b ->
+	bool Nothing (Just (bitsToBits 8 b, b `shiftR` 8)) (b /= zeroBits)
+
+fromBits' :: FiniteBits b => b -> LBS.ByteString
+fromBits' b0 = go (finiteBitSize b0 `div` 8) b0
+	where
+	go 0 _ = ""
+	go n b = bitsToBits 8 b `LBS.cons` go (n - 1) (b `shiftR` 8)
+
+toBits :: Bits b => LBS.ByteString -> b
+toBits = LBS.foldr (\b s -> bitsToBits 8 b .|. s `shiftL` 8) zeroBits
+
+toBits' :: forall b . FiniteBits b => LBS.ByteString -> Maybe b
+toBits' bs = bool
+	Nothing
+	(Just $ LBS.foldr (\b s -> bitsToBits 8 b .|. s `shiftL` 8) zeroBits bs)
+	(8 * LBS.length bs <= fromIntegral (finiteBitSize @b undefined))
+
+toBitsBE :: Bits b => LBS.ByteString -> b
+toBitsBE = LBS.foldl (\s b -> bitsToBits 8 b .|. s `shiftL` 8) zeroBits
+
+fromBitsBE' :: FiniteBits b => b -> LBS.ByteString
+fromBitsBE' b0 = go (finiteBitSize b0 `div` 8) b0
+	where
+	go 0 _ = ""
+	go n b = go (n - 1) (b `shiftR` 8) `LBS.snoc` bitsToBits 8 b
 
 splitAt' :: Int64 -> LBS.ByteString -> Maybe (LBS.ByteString, LBS.ByteString)
 splitAt' n bs
diff --git a/src/Data/ByteString/ToolsYj.hs b/src/Data/ByteString/ToolsYj.hs
--- a/src/Data/ByteString/ToolsYj.hs
+++ b/src/Data/ByteString/ToolsYj.hs
@@ -5,9 +5,17 @@
 
 module Data.ByteString.ToolsYj (
 
+	-- * FROM/TO BITS
+
 	fromBits, fromBits', toBits, toBits',
 
-	fromBitsBE', toBitsBE, splitAt'
+	-- * FROM/TO BITS -- BIG ENDIEN
+
+	fromBitsBE', toBitsBE,
+
+	-- * SPLIT AT
+
+	splitAt'
 
 	) where
 
diff --git a/tools-yj.cabal b/tools-yj.cabal
--- a/tools-yj.cabal
+++ b/tools-yj.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           tools-yj
-version:        0.1.0.30
+version:        0.1.0.31
 synopsis:       Tribial tools
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/tools-yj#readme>
 category:       Tools