Sliders of a movable lens holder are provided with cam followers respectively. Each of the sliders engages with a guide opening formed in a lens frame so that the movable lens holder is allowed to move in an optical-axis direction. The movable lens holder is retained in a cam barrel provided with cam grooves, which are formed so as to shift their positions in the optical-axis direction and in a rotational direction of the cam barrel. The cam followers engage with the cam grooves respectively.