A cam mechanism for a lens barrel includes a cam ring including at a cam groove which is open at one end; a support ring supporting an imaging component, the support ring having a cam follower engageable with the cam groove and movable therein towards and away from the open end, wherein the support ring is movable along an axis relative to the cam ring without rotation; and a movement limiter configured to stop or limit disengagement of the cam follower from the open end of the cam groove.