To obtain a positioning reference portion with good processing accuracy, which is formed of a newly-formed surface, a blank is press-molded by an upper mold, whereby a vertex portion abuts on an inner wall portion of a lower mold. In such a way, an oxide film that covers the vertex portion is broken by an internal pressure of the blank, and a raw material without oxide is moved by viscous flow from an inside thereof as illustrated by arrows. The raw material without oxide moved by viscous flow is thrust against the inner wall portion of the lower mold, whereby a newly-formed surface is formed, and this newly-formed surface serves as a positioning reference portion of an optical element. The newly-formed surface has surface roughness of the inner wall portion of the lower mold transferred thereto, and the positioning reference portion having good roughness is formed.