Provided is a method of molding an optical element. The method includes: inserting a neck portion provided in each of an upper mold and a lower mold into a hole portion provided in a side surface mold; replacing an atmosphere in the hole portion of the side surface mold with an inert gas through a groove communicating between either an upper end surface or a lower end surface of the side surface mold and the hole portion of the side surface mold; heating a molding material disposed in the hole portion of the side surface mold; and bringing the upper mold and the side surface mold, and the lower mold relatively close to each other to press molding the molding material to obtain an optical element.