A process cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The main assembly includes first and second rotatable main assembly drive transmission members. The cartridge includes an electrophotographic photosensitive drum, a developing roller, a drum coupling member, provided on one axial end of the drum, for engaging the first m transmission member and transmitting a first rotational driving force to the drum, when the cartridge is mounted to the main assembly, and a shaft coupler provided on one axial end of the developing roller, for transmitting a second rotational driving force with a deviation permitted between an axis of the second transmission member and an axis of the developing roller. The shaft coupler includes an engaging portion for engaging the second transmission member and receiving the second rotational driving force, when the cartridge is mounted to the main.