A cam mechanism of a lens barrel includes first and second ring members; cam grooves having similar cam diagrams formed on one of the first and second ring members, and cam followers formed on the other thereof. Two groove/follower groups positioned at different positions in a circumferential direction. The cam grooves of one of the two groove/follower groups intersect cam grooves of another of the two groove/follower groups, respectively. One of the following is satisfied: (a) a distance in the optical-axis direction between front and rear groove/follower sets of one of the two groove/follower groups is different from that between the front and rear groove/follower sets of another of the two groove/follower groups, and (b) a distance in the circumferential direction between two front groove/follower sets of the two groove/follower groups is different from that between two the rear groove/follower sets of the two groove/follower groups.