To easily regenerate a mold, which has been worn, with a proper clearance.

When the mold for molding a lens which is provided with a molding surface for forming an optical surface of the glass lens, a pair of cores each having a coating film formed at least on a molding surface and a drum mold sliding on the cores is repeatedly used to form a fresh coating film, the inner surface of the drum mold or the side surface of a base material 31 of a core is worn. In the base material 31 having the worn side surface, the coating film is removed while a cutting worked layer 32 on which an optical surface shape of a lens to be molded is accurately formed is left. An oxidation preventive film 43 to compensate for the wear of the base material 31 is formed on the molding surface of the cutting worked layer 32 and the worn side surface of the base material 31 to have a thickness to become D1 diameter before the wear as a regenerating coating film in the base material 31 on which the coating film is removed. A mold releasing film 38 is formed on the oxidation preventing film 43 to become a regenerated core.