An image forming apparatus includes a cartridge detachably mountable to a main assembly of the apparatus, the cartridge including a photosensitive drum, a drum frame supporting the drum, and a regulated portion for regulating rotation of the cartridge; a supporting member movable between an inside position an outer position; a moving member capable of taking a first position in which the moving member urges the regulated portion to space the drum from the transfer member and a second position in which the moving member to contact the drum to the transfer member; and a regulating portion for engaging with the regulated portion to regulate rotation of the cartridge when the moving member is in the second position, and for permitting movement of the supporting member between the outer position and the inside position with the regulating portion being in engagement with the regulated portion to limit rotation of the cartridge.