A first lens holder is connected with a rotary barrel through a helicoid mechanism, and moves in an optical axial direction when the rotary barrel rotates. A second lens holder is connected with the rotary barrel through a cam mechanism. The cam mechanism is constituted of a cam portion that is disposed on a front end surface of the rotary barrel and cam followers that are disposed on a rear end surface of the second lens holder. The cam portion is formed to have sloped surfaces inclined along a circumferential direction and these sloped surfaces are in contact with the cam followers. When the rotary barrel rotates, the cam followers shift in the optical axial direction along the sloped surfaces, thereby moving the second lens holder back and forth in the optical axial direction.