The present invention relates to a cartridge detachably mountable to a main assembly of an image forming apparatus. The cartridge comprises a photosensitive drum; a gear member at least a part of which is uncovered to receive a driving force from an outside of the cartridge; and a movable member provided on the same side of the cartridge as the gear member in the axial direction of the photosensitive drum, the movable member having a portion a distance of which from the axis of the photosensitive drum is changeable, wherein as seen along the axis of the photosensitive drum, the movable member is movable between (a) a first position in which the portion of the movable member is adjacent to an outer peripheral surface of the photosensitive drum and (b) a second position in which the portion of the movable member is more remote from the axis of the photosensitive drum than when the movable member is in the first position, as viewed along the axis of the photosensitive drum. When the movable member is in the first position, the portion of the movable member faces an uncovered portion of the gear member with the photosensitive drum interposed therebetween. The movable member is configured such that the portion of the movable member is away from the uncovered portion of the gear member.