A process cartridge, detachably mountable to a main assembly of an electrophotographic image forming apparatus includes an electrophotographic photosensitive drum; a developer accommodating portion; a developing roller for developing a latent image formed on the drum using the developer accommodated in the accommodating portion; a developer supply roller; a developing device frame supporting the developing roller and the developer supply roller and having the developer accommodating portion; a first gear having a driving force receiving gear portion which is engaged with a main assembly gear when the process cartridge is mounted to the main assembly; a second gear provided inside the driving force receiving gear portion in a longitudinal direction of the developing device frame and being effective to transmit the driving force received by the first gear to the developer supply roller; and a supporting member, disposed between the first gear and the second gear with respect to the longitudinal direction of the developing device frame, for supporting the second gear.