A cam mechanism includes a cam ring, and a linearly movable frame supporting an optical element. Cam groove groups are located at different positions in a circumferential direction on the cam ring, and each cam groove group includes cam grooves at different positions in the optical-axis direction and trace the same reference cam diagram. A cam groove intersects another cam groove of another cam groove group adjacent thereto in the circumferential direction. Each cam follower group includes cam followers located at different positions in the optical-axis direction engageable with the cam grooves of each cam groove group. In each cam groove group, at least one complementing cam follower of each cam follower group remains engaged in a corresponding cam groove when another cam follower of the complementing cam followers passes through an intersection area of the intersecting cam grooves during a rotation of the cam ring.