A developing cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus, said apparatus comprising: a cartridge frame; a developing roller for developing an electrostatic latent image formed on an electrophotographic photosensitive drum; an one-end frame groove provided at one longitudinal end of said cartridge frame; one-end bearing member for rotatably supporting one-end shaft provided at one longitudinal end of said developing roller extended in a longitudinal direction of said cartridge frame; an one-end bearing member cylinder, provided on said one-end bearing member, engaged with an inner surface of said one-end frame groove; a first projection provided on an outer surface of said one-end bearing member opposite from an inner side surface (a) on which said one-end bearing member cylinder is provided; a second projection which is provided on said one-end bearing member and which supports a gear for receiving a driving force from a main assembly of the apparatus when said cartridge is mounted to the main assembly of the apparatus; a first screw (335, 336) for securing said one-end bearing member to one end of said cartridge frame; an one-end side cover provided at one longitudinal end of said cartridge frame and covering said one-end bearing member; a second screw for securing said one-end side cover to one end of said cartridge frame; a third screw for securing said one-end side cover to said first projection provided on said one-end bearing member, characterized by an one-end frame projection provided at said one longitudinal end of said cartridge frame; an elongated bearing member opening which is provided on said one-end bearing member and through which said frame one end projection is penetrated; a first opening provided in said one-end side cover and engageable with said first projection; a second opening provided in said one-end side cover and engageable with said second projection; and an one-end side cover projection provided inside said one-end side cover and engageable with an inner surface of a one-end bearing member cylinder engaged with said one-end frame groove, wherein the first and second projection (340dd, 340cc) are made from metal. a cartridge frame; a developing roller for developing an electrostatic latent image formed on an electrophotographic photosensitive drum; an one-end frame groove provided at one longitudinal end of said cartridge frame; one-end bearing member for rotatably supporting one-end shaft provided at one longitudinal end of said developing roller extended in a longitudinal direction of said cartridge frame; an one-end bearing member cylinder, provided on said one-end bearing member, engaged with an inner surface of said one-end frame groove; a first projection provided on an outer surface of said one-end bearing member opposite from an inner side surface (a) on which said one-end bearing member cylinder is provided; a second projection which is provided on said one-end bearing member and which supports a gear for receiving a driving force from a main assembly of the apparatus when said cartridge is mounted to the main assembly of the apparatus; a first screw (335, 336) for securing said one-end bearing member to one end of said cartridge frame; an one-end side cover provided at one longitudinal end of said cartridge frame and covering said one-end bearing member; a second screw for securing said one-end side cover to one end of said cartridge frame; a third screw for securing said one-end side cover to said first projection provided on said one-end bearing member, characterized by an one-end frame projection provided at said one longitudinal end of said cartridge frame; an elongated bearing member opening which is provided on said one-end bearing member and through which said frame one end projection is penetrated; a first opening provided in said one-end side cover and engageable with said first projection; a second opening provided in said one-end side cover and engageable with said second projection; and an one-end side cover projection provided inside said one-end side cover and engageable with an inner surface of a one-end bearing member cylinder engaged with said one-end frame groove, wherein the first and second projection (340dd, 340cc) are made from metal.