The lens barrel includes a lens frame and a cam frame. The lens frame has a body supporting a lens element in the optical system, at least three through-holes formed in the lens frame body, at least three cam members arranged on the lens frame body and at least one protruding member that protrude from the lens frame body. The cam frame has a body, at least three projection members extending from the cam frame body and inserted through the through-holes, at least three cam grooves formed in the cam frame body and the projection members to guide the cam members and to movably support the lens frame with respect to the cam frame body. The cam frame also has at least one auxiliary groove to guide the protruding member. One end of the auxiliary groove is disposed in the circumferential direction between two adjacent projection members.