An electrophotographic image forming apparatus for forming an image on a recording material includes an electrophotographic photosensitive drum and a developing cartridge including a developing roller for developing an electrostatic latent image formed on the electrophotographic photosensitive drum. A cartridge supporting member is movable, while detachably mounting the developing cartridge, between an inside position which is inside of the main assembly of the apparatus to mount the developing cartridge to the main assembly of the apparatus and an outside position that is outside of the main assembly of the apparatus to remove the developing cartridge from the main assembly of the apparatus.