diff --git a/src/Graphics/X11/Turtle.hs b/src/Graphics/X11/Turtle.hs
--- a/src/Graphics/X11/Turtle.hs
+++ b/src/Graphics/X11/Turtle.hs
@@ -53,11 +53,26 @@
 	(x, y) <- position
 	return $ ((x - x0) ** 2 + (y - y0) ** 2) ** (1 / 2)
 
-pastDrawLines :: IORef [Maybe (((Double, Double), Double), IO ())]
+pastDrawLines :: IORef [Maybe (((Double, Double), Double), Buf -> IO ())]
 pastDrawLines = unsafePerformIO $ newIORef []
 
+putToPastDrawLines :: (Double, Double) -> Double -> (Buf -> IO ()) -> IO ()
+putToPastDrawLines tpos tdir dl = do
+	pdls <- readIORef pastDrawLines
+	if length pdls < 300
+		then do
+			writeIORef pastDrawLines $ pdls ++ [Just ((tpos, tdir), dl)]
+		else do
+			maybe (return ()) (($ UndoBuf) . snd) $ head pdls
+			writeIORef pastDrawLines $ tail pdls ++ [Just ((tpos, tdir), dl)]
+
+setUndoPoint :: IO ()
+setUndoPoint = modifyIORef pastDrawLines $ (++ [Nothing])
+
 data PenState = PenUp | PenDown
 
+data Order = Forward Double | Left Double | Undo deriving Show
+
 doesPenDown :: PenState -> Bool
 doesPenDown PenUp = False
 doesPenDown PenDown = True
@@ -89,6 +104,15 @@
 			_ -> error $ "not implemented for event " ++ show ev
 	closeTurtle
 
+orderChan :: IORef (Chan Order)
+orderChan = unsafePerformIO $ newChan >>= newIORef
+
+getOrders :: IO [Order]
+getOrders = unsafeInterleaveIO $ do
+	o <- readIORef orderChan >>= readChan
+	os <- getOrders
+	return $ o : os
+
 initTurtle :: IO ()
 initTurtle = do
 	w <- openWorld
@@ -117,7 +141,7 @@
 	width <- windowWidth
 	height <- windowHeight
 	rawGoto (x + width / 2) (- y + height / 2)
-		>> modifyIORef pastDrawLines (++ [Nothing])
+		>> setUndoPoint
 rawGoto xTo yTo = do
 	w <- readIORef world
 	(x0, y0) <- getCursorPos w
@@ -143,7 +167,7 @@
 	flushWorld w
 
 forward, rawForward :: Double -> IO ()
-forward len = rawForward len >> modifyIORef pastDrawLines (++ [Nothing])
+forward len = rawForward len >> setUndoPoint
 rawForward len = do
 	w <- readIORef world
 	(x0, y0) <- getCursorPos w
@@ -171,13 +195,13 @@
 
 drawLine :: World -> Double -> Double -> Double -> Double -> IO ()
 drawLine w x1 y1 x2 y2 = do
-	let act = do
+	let act buf = do
 		ps <- readIORef penState
 		when (doesPenDown ps) $
-			lineToBG w (round x1) (round y1) (round x2) (round y2)
-	act
+			lineToBG w buf (round x1) (round y1) (round x2) (round y2)
+	act BG
 	dir <- readIORef world >>= getCursorDir 
-	modifyIORef pastDrawLines (++ [Just (((x2, y2), dir), act)])
+	putToPastDrawLines (x2, y2) dir act
 
 redrawLines :: IO ()
 redrawLines = do
@@ -185,7 +209,7 @@
 	dls <- fmap (map fromJust . filter isJust) $ readIORef pastDrawLines
 	clear
 	flip mapM_ dls $ \dl -> do
-		snd dl
+		snd dl BG
 		drawWorld w
 		flushWorld w
 		threadDelay 20000
@@ -194,9 +218,10 @@
 undoAll = do
 	w <- readIORef world
 	dls <- fmap (map fromJust . filter isJust) $ readIORef pastDrawLines
-	flip mapM_ (zip (reverse $ map fst dls) $ map sequence_ $ reverse $ inits $ map snd dls)
+	flip mapM_ (zip (reverse $ map fst dls) $ map sequence_ $ reverse $ inits
+		$ map (($ BG) . snd) dls)
 		$ \((pos, dir), dl) -> do
-		cleanBG w
+		cleanBG w BG
 		dl
 		uncurry (setCursorPos w) pos
 		setCursorDir w dir
@@ -213,9 +238,11 @@
 		draw1 = map fromJust $ filter isJust $ head
 			$ dropWhile (isJust . last) $ reverse $ inits dls
 		draw' = draw ++ [draw1]
-	flip mapM_ (zip (reverse $ map (fst . fromJust) $ filter isJust dls ) $ map sequence_
-		$ map (map snd) draw') $ \((pos, dir), dl) -> do
-		cleanBG w
+	flip mapM_ (zip (reverse $ map (fst . fromJust) $ filter isJust dls )
+		$ map sequence_
+		$ map (map (($ BG) . snd)) draw') $ \((pos, dir), dl) -> do
+		cleanBG w BG
+		undoBufToBG w
 		dl
 		uncurry (setCursorPos w) pos
 		setCursorDir w dir
@@ -233,7 +260,7 @@
 	drawWorld w
 	flushWorld w
 	pos <- getCursorPos w
-	modifyIORef pastDrawLines (++ [Just ((pos, nd), return ())])
+	putToPastDrawLines pos nd $ const (return ())
 
 rotateTo :: Double -> IO ()
 rotateTo d = do
@@ -248,7 +275,7 @@
 	flushWorld w
 
 rotate, rawRotate :: Double -> IO ()
-rotate d = rawRotate d >> modifyIORef pastDrawLines (++ [Nothing])
+rotate d = rawRotate d >> setUndoPoint
 rawRotate d = do
 	w <- readIORef world
 	d0 <- getCursorDir w
@@ -281,11 +308,11 @@
 clear :: IO ()
 clear = do
 	w <- readIORef world
-	cleanBG w
+	cleanBG w BG
 	drawWorld w >> flushWorld w
 	pos <- getCursorPos w
 	dir <- getCursorDir w
-	modifyIORef pastDrawLines (++ [Just ((pos, dir), cleanBG w)])
+	putToPastDrawLines pos dir $ cleanBG w
 
 closeTurtle :: IO ()
 closeTurtle = readIORef world >>= closeWorld
diff --git a/src/Graphics/X11/World.hs b/src/Graphics/X11/World.hs
--- a/src/Graphics/X11/World.hs
+++ b/src/Graphics/X11/World.hs
@@ -8,6 +8,7 @@
 	setCursorSize,
 	setCursorShape,
 	drawWorld,
+	undoBufToBG,
 	closeWorld,
 	withEvent,
 	flushWorld,
@@ -17,6 +18,7 @@
 	lineToBG,
 	cleanBG,
 	getWindowSize,
+	Buf(..),
 
 	Event(..),
 	Position,
@@ -40,6 +42,7 @@
 	wDel :: Atom,
 	wBG :: Pixmap,
 	wBuf :: Pixmap,
+	wUndoBuf :: Pixmap,
 	wPos :: IORef (Double, Double),
 	wDir :: IORef Double,
 	wSize :: IORef Double,
@@ -100,11 +103,13 @@
 	win <- createSimpleWindow dpy root 0 0 width height 1 black white
 	bg <- createPixmap dpy root width height $ defaultDepth dpy scr
 	buf <- createPixmap dpy root width height $ defaultDepth dpy scr
+	undoBuf <- createPixmap dpy root width height $ defaultDepth dpy scr
 	gc <- createGC dpy win
 	gc' <- createGC dpy win
 	setForeground dpy gc' 0xffffff
 	fillRectangle dpy bg gc' 0 0 width height
 	fillRectangle dpy buf gc' 0 0 width height
+	fillRectangle dpy undoBuf gc' 0 0 width height
 	setWMProtocols dpy win [del]
 	selectInput dpy win $ exposureMask .|. keyPressMask
 	mapWindow dpy win
@@ -113,7 +118,7 @@
 	initDir <- newIORef undefined
 	initSize <- newIORef undefined
 	initShape <- newIORef undefined
-	return $ World dpy win gc del bg buf initPos initDir initSize initShape
+	return $ World dpy win gc del bg buf undoBuf initPos initDir initSize initShape
 
 closeWorld :: World -> IO ()
 closeWorld = closeDisplay . wDisplay
@@ -129,6 +134,12 @@
 	displayCursor w s d x y
 	copyArea (wDisplay w) (wBuf w) (wWindow w) (wGC w) 0 0 width height 0 0
 
+undoBufToBG :: World -> IO ()
+undoBufToBG w = do
+	(_, _, _, width, height, _, _) <- getGeometry (wDisplay w) (wWindow w)
+	copyArea (wDisplay w) (wUndoBuf w) (wBG w) (wGC w) 0 0 width height 0 0
+
+
 withEvent :: World -> s -> (s -> Event -> IO (s, Bool)) -> IO s
 withEvent w stat0 act = doWhile stat0 $ \stat -> allocaXEvent $ \e -> do
 	nextEvent (wDisplay w) e
@@ -146,15 +157,21 @@
 makeFilledPolygonCursor w ps =
 	fillPolygon (wDisplay w) (wBuf w) (wGC w) ps nonconvex coordModeOrigin
 
-lineToBG :: World -> Position -> Position -> Position -> Position -> IO ()
-lineToBG w x1 y1 x2 y2 = drawLine (wDisplay w) (wBG w) (wGC w) x1 y1 x2 y2
+data Buf = BG | UndoBuf
 
-cleanBG :: World -> IO ()
-cleanBG w = do
+lineToBG :: World -> Buf -> Position -> Position -> Position -> Position -> IO ()
+lineToBG w BG x1 y1 x2 y2 = drawLine (wDisplay w) (wBG w) (wGC w) x1 y1 x2 y2
+lineToBG w UndoBuf x1 y1 x2 y2 = drawLine (wDisplay w) (wUndoBuf w) (wGC w) x1 y1 x2 y2
+
+cleanBG :: World -> Buf -> IO ()
+cleanBG w b = do
 	(_, _, _, width, height, _, _) <- getGeometry (wDisplay w) (wWindow w)
 	gc <- createGC (wDisplay w) (wWindow w)
 	setForeground (wDisplay w) gc 0xffffff
-	fillRectangle (wDisplay w) (wBG w) gc 0 0 width height
+	let buf = case b of
+		BG -> wBG w
+		UndoBuf -> wUndoBuf w
+	fillRectangle (wDisplay w) buf gc 0 0 width height
 
 flushWorld :: World -> IO ()
 flushWorld = flush . wDisplay
diff --git a/xturtle.cabal b/xturtle.cabal
--- a/xturtle.cabal
+++ b/xturtle.cabal
@@ -2,7 +2,7 @@
 cabal-version:	>= 1.6
 
 name:		xturtle
-version:	0.0.1
+version:	0.0.2
 stability:	experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>