A drum supporting member, which is usable with an image forming apparatus, includes a photosensitive drum and a mounting portion for detachably mounting a developing cartridge. The drum mounting portion also includes a contacting member contactable with the developing cartridge, with contacting member being movable between a first position and a second position. When the contacting member is in the first position, the contacting member contacts the developing cartridge with a developing roller of the developing cartridge being placed in a third position contacting the photosensitive drum. When the contacting member is in the second position, the contacting member contacts the developing cartridge with the developing cartridge being placed in a fourth position in which the developing cartridge is dismountable from the drum supporting member.