An image forming apparatus includes a transfer belt stretched around driving and blade opposing rollers. The blade opposing roller is biased in a bias direction away from the driving roller by a biasing member and has a cleaning blade in contact with the belt. In a color mode, the belt is thrust against multiple image forming stations using multiple transfer members. In a monochromatic model, the belt is thrust against only a monochromatic image forming station using a monochromatic transfer member and other transfer members are moved away from the image forming stations. The belt is brought into a thrust-condition after completion of the monochromatic mode to be thrust against multiple image forming stations; and is then released to bring the blade opposing roller into following rotation in the opposite direction of the transport direction so that the blade opposing roller is biased in the bias direction.