ve is subjected to plating processing, etc. with nickel or other material to be a thickness of, for example, 0.3 to 0.5 mm, so that a master stamper 12 is formed. [0021] An electric plating method featuring a rapid growth rate in plating is used for the nickel plating processing, but since it is necessary that the surface of the master disk for mastering has to be conductive in advance, a nickel t