A cam mechanism for a lens barrel includes an annular member which is linearly
guided along an optical axis, and having a cam follower on an outer peripheral
surface; a cam ring having a cam groove on an inner peripheral surface including
a photographing section and an accommodation section, the cam follower being engaged
in the cam groove; and a biasing device for biasing the annular member forward
to normally press the cam follower against a front cam surface in the cam groove.
A rear end portion of the cam groove is open at a rear end surface of the cam ring
to serve as the accommodation section, and the cam follower is disengageable from
the front cam surface in the cam groove against a biasing force of the biasing
device when the cam follower is engaged in the accommodation section.
