Image forming apparatus having reduced manufacturing costs, and image forming unit and developing unit included therein

An image forming apparatus supplies toner to an electrostatic latent image on a circumferential surface of a photosensitive rotating member to develop the electrostatic latent image, and includes: a photosensitive unit including the photosensitive rotating member and a pair of support frames rotatably supporting the photosensitive rotating member at its axial ends; a developing unit including a developing sleeve that is longer in its rotational axis direction than an element tube of the photosensitive rotating member in its rotational axis direction, and a pair of bearings provided outward from axial ends of the element tube and rotatably holding the developing sleeve at its axial ends; and a forcing member relatively forcing the developing unit toward the photosensitive unit to bring the bearings into abutment with the respective support frames, such that a gap between the developing sleeve and the photosensitive rotating member is maintained at a predetermined value.