A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus includes a positioning portion for positioning the process cartridge when mounted to a mounting position of the main assembly. The positioning portion is engageable with a positioning member provided in the main assembly of the apparatus, and is projected from the cartridge coaxially with and at one longitudinal end side of a electrophotographic photosensitive drum. A drum driving force receiving member receives driving force for rotating the drum from the main assembly when the process cartridge is mounted, the drum driving force receiving member being juxtaposed with the positioning member coaxially with the drum and projected outwardly beyond the positioning member. A transporting member driving force receiving member receives driving force for rotating a toner transporting member from the main assembly when the process cartridge is mounted, wherein the transporting member driving force receiving member is disposed at the same side as the drum driving force receiving member disposed in a longitudinal direction of the drum.