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.