A cartridge is detachably mountable to a main assembly of an electrophotographic image forming apparatus. The cartridge includes coupling member that is provided for receiving a rotational force for rotating a developing roller, with a cylindrical member movably supporting one end portion of the coupling member inside of the cylindrical member, and a cylindrical member side force receiving portion being provided inside the cylindrical member for receiving the rotational force received by the coupling member. The cartridge further includes a first regulating portion for preventing one end portion of the coupling member from disengaging in an axial direction of the cylindrical member; and a second regulating portion for regulating deformation of the first regulating portion in a state in which one end portion of the coupling member is mounted to an inside of the cylindrical member with deformation of the first regulating portion.