An image forming apparatus includes photosensitive drums, a transfer belt having an outer surface facing the photosensitive drums, a tension roller in contact with an inner surface of the transfer belt, a cam in contact with the tension roller and movable to a first position to increase the tension to the transfer belt and a second position to decrease the tension to the transfer belt, a support having a supporting surface facing the outer surface of the transfer belt, and a lever mechanically linked to the cam and the support and rotatable from a third position at which the cam is in the first position to a fourth position at which the cam is in the second position. As the lever is moved from the third to the fourth position, the supporting surface is raised against the outer surface of the transfer belt.