a process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus including an electrophotographic photosensitive drum , a process device actable on the drum , a cartridge positioning portion for engaging a main assembly positioning portion to position the cartridge with respect to a direction crossing the direction of the axis of the drum when the cartridge is mounted to the main assembly in a direction parallel with the axis of the photosensitive drum , and a movable member movable between a first position contacting the main assembly in the process of mounting of the cartridge to the main assembly , and a second position contacting a main assembly urging member and receiving a force in the crossing direction to contact the cartridge positioning portion to the main assembly positioning portion to position the cartridge in the crossing direction , when the cartridge is mounted to the main assembly .