A cartridge is configured to supply developing agent to a peripheral surface of a photosensitive drum. The cartridge includes a frame, a developing roller and first and second side seal members. The developing roller defines an axial direction, and is configured to supply developing agent in the frame to the photosensitive drum. The first side seal member is configured to seal a boundary between the frame and one end portion of the developing roller in the axial direction. The second side seal member is configured to seal a boundary between the frame and another end portion of the developing roller. The first and second side seal members define a gap therebetween in the axial direction, and the gap has a gap length smaller than a width in the axial direction of a maximum width sheet conveyed to the photosensitive drum.