A drum unit usable with a process cartridge includes a photosensitive drum having an axis L1; and a coupling member having an axis L2 and connected to an end portion of the photosensitive drum, the coupling member being provided with a projection extending toward an end portion of the coupling member, wherein the coupling member is movable along the axis L2 between a first position, and a second position in which the projection is closer to the photosensitive drum than in the first position, wherein the projection is provided with a force receiving portion for receiving a rotational force and an outer surface facing away from the axis L2, and wherein at least a part of the outer surface is more distant from the axis L2 as is further from the photosensitive drum in a direction of the axis L1.