To reduce the size and cost of a cam cylinder.

An abutting member 48 for abutting on the rear end 41a of the cam cylinder 41 is disposed at the rear end of a fixed cylinder 40. An annular groove 49 is formed in the periphery of the fixed cylinder 40 and in a position near the front of the front end 41b of the cam cylinder 41 abutting on the abutting member 48. An O-ring 50 is fitted in the annular groove 49 while the O-ring 50 is in contact with the front end 41b of the cam cylinder 41. The O-ring 50 engages with the side wall of the annular groove 49, which is on the fixed-cylinder front side, and movement of the O-ring to the fixed-cylinder front side is restricted to thereby restrict movement of the cam cylinder 41 in the direction of an optical axis. This eliminates the need to provide a restriction hole or restriction roller used to restrict movement of the cam cylinder 41 in the direction of the optical axis. Accordingly, the size and cost of the cam cylinder 41 can be reduced.