diff --git a/src/common/othello/ai/back.ts b/src/common/othello/ai/back.ts
index 9765b7d4e..38a564f55 100644
--- a/src/common/othello/ai/back.ts
+++ b/src/common/othello/ai/back.ts
@@ -135,7 +135,7 @@ function onGameStarted(g) {
 }
 
 function onSet(x) {
-	o.put(x.color, x.pos, true);
+	o.put(x.color, x.pos);
 
 	if (x.next === botColor) {
 		think();
@@ -157,17 +157,17 @@ function think() {
 	 */
 	const dive = (o: Othello, pos: number, alpha = -Infinity, beta = Infinity, depth = 0): number => {
 		// 試し打ち
-		const undo = o.put(o.turn, pos, true);
+		o.put(o.turn, pos);
 
 		const key = o.board.toString();
 		let cache = db[key];
 		if (cache) {
 			if (alpha >= cache.upper) {
-				o.undo(undo);
+				o.undo();
 				return cache.upper;
 			}
 			if (beta <= cache.lower) {
-				o.undo(undo);
+				o.undo();
 				return cache.lower;
 			}
 			alpha = Math.max(alpha, cache.lower);
@@ -199,7 +199,7 @@ function think() {
 			}
 
 			// 巻き戻し
-			o.undo(undo);
+			o.undo();
 
 			// 接待なら自分が負けた方が高スコア
 			return isSettai
@@ -225,7 +225,7 @@ function think() {
 			});
 
 			// 巻き戻し
-			o.undo(undo);
+			o.undo();
 
 			// ロセオならスコアを反転
 			if (game.settings.is_llotheo) score = -score;
@@ -257,7 +257,7 @@ function think() {
 			}
 
 			// 巻き戻し
-			o.undo(undo);
+			o.undo();
 
 			if (value <= alpha) {
 				cache.upper = value;
diff --git a/src/common/othello/core.ts b/src/common/othello/core.ts
index 5e25578ca..217066d37 100644
--- a/src/common/othello/core.ts
+++ b/src/common/othello/core.ts
@@ -50,6 +50,8 @@ export default class Othello {
 	public prevPos = -1;
 	public prevColor: Color = null;
 
+	private logs: Undo[] = [];
+
 	/**
 	 * ゲームを初期化します
 	 */
@@ -138,13 +140,7 @@ export default class Othello {
 	 * @param color 石の色
 	 * @param pos 位置
 	 */
-	public put(color: Color, pos: number, fast = false): Undo {
-		if (!fast && !this.canPut(color, pos)) {
-			console.warn('can not put this position:', pos, color);
-			console.warn(this.board);
-			return null;
-		}
-
+	public put(color: Color, pos: number) {
 		this.prevPos = pos;
 		this.prevColor = color;
 
@@ -160,14 +156,14 @@ export default class Othello {
 
 		const turn = this.turn;
 
-		this.calcTurn();
-
-		return {
+		this.logs.push({
 			color,
 			pos,
 			effects,
 			turn
-		};
+		});
+
+		this.calcTurn();
 	}
 
 	private calcTurn() {
@@ -181,7 +177,8 @@ export default class Othello {
 		}
 	}
 
-	public undo(undo: Undo) {
+	public undo() {
+		const undo = this.logs.pop();
 		this.prevColor = undo.color;
 		this.prevPos = undo.pos;
 		this.board[undo.pos] = null;