A lens barrel that enables to increase a degree of freedom for selecting positions of grooves on a cam barrel. A lens holding member holds a lens and has a follower part. A rectilinear barrel regulates relative rotation of the lens holding member and has a bayonet convex part. The cam barrel has a cam groove with which the follower part engages and a bayonet groove with which the bayonet convex part engages. The positional relationship between the cam barrel and the rectilinear barrel in the optical axis direction is regulated because the bayonet convex part contacts the wall surfaces of both sides of the bayonet groove in a WIDE position, and because a section between a wall surface of the bayonet groove and the end face of the cam barrel is pinched between the bayonet convex part and a member provided in the rectilinear barrel in a TELE position.