A cartridge includes a casing, a rotatable member rotatably supported by the casing, a protruding member configured to advance and retract in directions parallel to an axis of rotation of the rotatable member, and an urging member configured to urge the protruding member to advance in an advancing direction. The protruding member has a particular sloping surface configured to be contacted in a direction orthogonal to an axis of rotation of the protruding member when the cartridge is mounted. The particular sloping surface slopes with respect to directions parallel to and orthogonal to the axis of rotation of the protruding member.