A belt is looped around a plurality of rollers including a drive roller and a follow roller. The belt has an inner peripheral surface facing inside of a loop of the belt and an outer peripheral surface opposite the inner peripheral surface. The belt has a first widthwise edge and a second widthwise edge. A widthwise-movement restricting member is disposed on the inner peripheral surface on a first widthwise edge side. The widthwise-movement restricting member restricts widthwise movement of the belt in a direction toward a second widthwise edge side. An expansion-contraction restricting member is disposed on the second widthwise edge side on at least one of the inner peripheral surface and the outer peripheral surface. The expansion-contraction restricting member is less expandable in a peripheral direction of the belt than the widthwise-movement restricting member is. An urging member applies tension to the belt in the peripheral direction.