A process cartridge (7, 7a-7d) detachably mountable to a main assembly of an electrophotographic image forming apparatus, said image forming apparatus including a cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) movable between a first position and a second position away from said first position, said process cartridge (7, 7a-7d) comprising: an electrophotographic photosensitive drum; a developing roller, contacted to the electrophotographic photosensitive drum, for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a first frame (50, 50a-50d) for supporting said electrophotographic photosensitive drum; a second frame for supporting said developing roller, said second frame being connected with said first frame (50, 50a-50d) for relative rotation about a shaft which is disposed downstream of said developing roller with respect to a mounting direction in which said process cartridge (7, 7a-7d) is mounted to a main assembly of the apparatus; a first side wall provided at one end of the second frame (4, 4a-4d) in a longitudinal direction of said electrophotographic photosensitive drum, an entering portion (45a, 45b), provided at the first side wall (45h, 45j) and disposed downstream of said shaft with respect to the mounting direction, for permitting at least a part of the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) with respect to the longitudinal direction to enter when said process cartridge (7, 7a-7d) is mounted to the main assembly of the apparatus; and a cam engaging portion (46e, 46f) adapted to be engaged by the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) to receive a force from the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) for spacing said electrophotographic photosensitive drum and said developing roller from each other, characterized in that said cam engaging portion (46e, 46f) is disposed at the first side wall and downstream of said entering portion (45a, 45b) with respect to the mounting direction, and projects from one of the lengthwise ends of the second frame in terms of a direction parallel to the lengthwise direction of the photosensitive drum. an electrophotographic photosensitive drum; a developing roller, contacted to the electrophotographic photosensitive drum, for developing an electrostatic latent image formed on said electrophotographic photosensitive drum; a first frame (50, 50a-50d) for supporting said electrophotographic photosensitive drum; a second frame for supporting said developing roller, said second frame being connected with said first frame (50, 50a-50d) for relative rotation about a shaft which is disposed downstream of said developing roller with respect to a mounting direction in which said process cartridge (7, 7a-7d) is mounted to a main assembly of the apparatus; a first side wall provided at one end of the second frame (4, 4a-4d) in a longitudinal direction of said electrophotographic photosensitive drum, an entering portion (45a, 45b), provided at the first side wall (45h, 45j) and disposed downstream of said shaft with respect to the mounting direction, for permitting at least a part of the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) with respect to the longitudinal direction to enter when said process cartridge (7, 7a-7d) is mounted to the main assembly of the apparatus; and a cam engaging portion (46e, 46f) adapted to be engaged by the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) to receive a force from the cam member (8R, 8Ra-8Rd, 8L, 8La-8Ld) for spacing said electrophotographic photosensitive drum and said developing roller from each other, characterized in that said cam engaging portion (46e, 46f) is disposed at the first side wall and downstream of said entering portion (45a, 45b) with respect to the mounting direction, and projects from one of the lengthwise ends of the second frame in terms of a direction parallel to the lengthwise direction of the photosensitive drum.