A lens held by a lens holding member is centered easily and correctly by a mechanism in which a guide pin is inserted into a guide hole for positioning the lens holding member with respect to the main body unit of the lens barrel in a plane perpendicular to the optical axis of the lens and for mounting the lens holding member for movement in a direction along the optical axis. Adjustment pins are rotationally mounted on at least three sites on the outer peripheral surface of the main body unit of the lens barrel. If each adjustment pin is rotated, an offset portion of the adjustment pin which is relative to the center of rotation of the adjustment pin, is rotated, as the offset portion is engaged in an engagement hole of the lens holding member. In this way the lens holding member on each site is displaced in the direction along the optical axis to adjust the tilt of the lens held by the lens holding member.