A pre-curing viscous solution (precursor solution) is applied to the back surface of a substrate for forming an optically transparent layer principally composed of an inorganic material. The substrate is heated or irradiated with UV light while being pressed with unevenness of a mold. By removing the substrate from the mold, the optically transparent, inorganic material layer principally composed of the inorganic material is formed on the substrate. In this manner, the inorganic material layer with the unevenness is formed on the back surface of the substrate (a light extraction surface) by embossing.