A metal layer is formed on a highly light-transmissive substrate; a resist mask having an opening pattern is formed on the metal layer; exposed portions of the metal layer is etched away in this state to form openings; then the resist mask is removed; and a surface of the metal layer and an inner side wall of each of the openings are oxidized to form a metal oxide layer. Thus, a front surface and a rear surface of the aperture plate are caused to have different reflectances. The oxide layer is formed at the same time as when the resist mask is ashed to remove resist.