To provide an apparatus for driving a photosensitive member or the like, which is capable of reducing vibration in a belt advancing direction by a small-sized inertia body, saving space of the whole apparatus, preventing an image quality from deteriorating due to the vibration, and reducing vibration in a direction perpendicular to the belt advancing direction and reducing noises.

A rotation-driving force is transmitted to a photosensitive member 1 (rotational body) through a belt 6. A tension roller 8 exerting tension to the belt 6 is provided with a fly wheel 9 (inertia body). This reduces the belt advancing direction resonance frequency resulting from the vibration occurring when the belt 6 and the pulleys 6, 7 mesh with each other. The diameter of the tension roller 8 is made smaller than that of the photosensitive element driving pulley 7 or the like, thereby enabling the fly wheel 9 to rotate in a high speed, which provides a large inertia effect.