A process cartridge detachably mountable to an electrophotographic image forming apparatus, said process cartridge comprising: an electrophotographic photosensitive drum extending in a longitudinal direction of said process cartridge; a first frame supporting said electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a second frame (45a, 45b) supporting said developing roller, said second frame (45a, 45b) being rotatable relative to said first frame; a first cartridge positioning portion which is provided at each of one and the other longitudinal end portion of said first frame and which is abuttable to a first main assembly positioning portion provided in the main assembly of the apparatus to position said process cartridge with respect to a direction crossing with the longitudinal direction when said process cartridge is mounted to the main assembly of the apparatus; a drive input gear, provided at said one longitudinal end portion of said second frame (45a, 45b), for engagement with a main assembly driving gear provided in the main assembly to transmit a rotational driving force to said developing roller; a second cartridge positioning portion which is provided at one longitudinal end portion of said first frame and which is abuttable to a second main assembly positioning portion provided in the main assembly of the apparatus to limit rotation of said process cartridge about said first cartridge positioning portion when said drive input gear receives said rotational driving force for rotating said developing roller from the main assembly of the apparatus; characterized in that a range of engagement (z), with respect to the longitudinal direction, between the main assembly driving gear and said drive input gear when said drive input gear is engaged with said main assembly driving gear, overlaps with said second cartridge positioning portion as seen in a direction which is perpendicular to the longitudinal direction and which passes through said second cartridge positioning portion. an electrophotographic photosensitive drum extending in a longitudinal direction of said process cartridge; a first frame supporting said electrophotographic photosensitive drum; a developing roller for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a second frame (45a, 45b) supporting said developing roller, said second frame (45a, 45b) being rotatable relative to said first frame; a first cartridge positioning portion which is provided at each of one and the other longitudinal end portion of said first frame and which is abuttable to a first main assembly positioning portion provided in the main assembly of the apparatus to position said process cartridge with respect to a direction crossing with the longitudinal direction when said process cartridge is mounted to the main assembly of the apparatus; a drive input gear, provided at said one longitudinal end portion of said second frame (45a, 45b), for engagement with a main assembly driving gear provided in the main assembly to transmit a rotational driving force to said developing roller; a second cartridge positioning portion which is provided at one longitudinal end portion of said first frame and which is abuttable to a second main assembly positioning portion provided in the main assembly of the apparatus to limit rotation of said process cartridge about said first cartridge positioning portion when said drive input gear receives said rotational driving force for rotating said developing roller from the main assembly of the apparatus; characterized in that a range of engagement (z), with respect to the longitudinal direction, between the main assembly driving gear and said drive input gear when said drive input gear is engaged with said main assembly driving gear, overlaps with said second cartridge positioning portion as seen in a direction which is perpendicular to the longitudinal direction and which passes through said second cartridge positioning portion.