A process cartridge detachably mountable to an electrophotographic image forming includes an electrophotographic photosensitive drum; a developing roller; a first cartridge positioning portion abuttable to a first main assembly positioning portion provided in a main assembly of the apparatus to position the cartridge with respect to a direction crossing the longitudinal direction, when the cartridge is mounted to the main assembly; a second cartridge positioning portion abuttable to a second main assembly positioning portion provided in the main assembly to limit rotation of the cartridge about the first cartridge positioning portion, when the cartridge receives a rotational driving force for rotating the roller from the main assembly; and a first drive input gear, for engagement with a main assembly driving gear to transmit a rotational driving force to the roller.