This invention provides an optical element comprising: an optical functional section on a first surface of the optical element, the optical functional section having a fine structure; and a flange section formed on a periphery of the optical functional section, wherein the flange section has a heat shrinkage-inhibiting portion, which inhibits heat shrinkage of the optical element during molding in a direction perpendicular to an optical axis of the optical element. The invention further provides a method of molding the optical element, and a mold.