A process cartridge detachably mountable to a main assembly of an electrophotographic image forming apparatus including an electrophotographic photosensitive member; a developing member for developing a latent image formed on the photosensitive member; a toner accommodating portion for accommodating toner to be used for development of the latent image by the developing member; a toner stirring member for stirring the toner accommodated in the toner accommodating portion; a driving force transmission member for transmitting rotational driving force to the toner stirring member to rotate the stirring member; wherein the driving force transmission member is penetrated through an opening provided in the toner accommodating portion; a locking member, provided inside of the toner accommodating portion to prevent the driving force transmission member from dropping out of the toner accommodating portion through the opening; a driving member for driving the driving force transmission member, wherein the driving member is provided outside the toner accommodating portion; wherein the driving force is transmitted from the driving member to the driving force transmission member such that driving force transmission member receives thrust force toward the toner accommodating portion through a projection having an inclined surface extending in a direction crossing with a rotational direction of the driving member and an engaging portion engaging with the inclined surface of the projection.