A lens retaining barrel includes a cylindrical part for radially positioning a lens and an abutment for positioning the lens in the direction of the optical axis of the lens. The cylindrical part has a multiplicity of protrusions uniformly and circumferentially spaced around the interior thereof such that a circle inscribed within the protrusions has the same diameter as the outer diameter of the lens and has its center coincident with the optical axis of the lens. The abutment extends radially inwardly a greater extent than the protrusions and has a multiplicity of seats uniformly and circumferentially spaced around the abutment for receiving the lens. The seats have tops defining an envelope extending in a direction orthogonal to the optical axis of the lens. The lens is retained in position by each protrusion of the cylindrical part and each top of the seats and is adhered to the lens retaining barrel by an adhesive. By virtue of this construction, the lens retaining barrel is free from any eccentricity or tilt of the lens, has a higher mounting accuracy, and is easy to assemble for mounting.