an electrophotographic image forming apparatus includes a main assembly ; a cartridge including process means actable on an electrophotographic photosensitive member , the process cartridge being detachably mountable relative to the main assembly ; an opening , provided in the main assembly of the apparatus , for permitting mounting and demounting of the cartridge ; an openable member , provided in the main assembly of the apparatus , for openably closing the opening ; an exposure device , provided on the openable member , for exposing the electrophotographic photosensitive member ; the cartridge including a first unit , and a second unit pivotably connected with the first unit ; a first positioning portion provided in the main assembly of the apparatus , wherein the exposure device is provided with a second positioning portion for positioning between the exposure device and the second unit of the cartridge by engagement with the cartridge by closing the openable member .