A process cartridge is provided detachably mountable to a main assembly of an electrophotographic image forming apparatus. The process cartridge includes an electrophotographic photosensitive drum and a process device actable on the drum. The process cartridge also includes 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. Further, a movable member is provided 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.