float rotationAngle; const float circle = MathHelper.Pi * 2; const float speed = 4; protected override void Update(GameTime gameTime) { float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; Window.Title = elapsed.ToString(); rotationAngle += elapsed * speed; rotationAngle = rotationAngle % circle; //一周毎に値にリセットがかかる動作になる base.Update(gameTime); }