A method of manufacturing a cap including a top face ring having an opening on the center thereof and a peripheral wall extending from the outer peripheral edge of the top face ring and directly or indirectly attached to a housing . When the cap is injection molded, a molten resin is injected from a center gate of a cavity of a circular plate located on the opening of the top face ring, allowed to radially flow to fill a cavity of the top face ring, and allowed to further flow to fill a cavity of the peripheral wall to form a molded body.
