After an external shape of a photoresist layer is patterned with use of a Cr film as an underlayer, i.e., a metal film to serve as an anticorrosive film that resists crystal etching, and an Au film as a surface layer, the Au film is etched. After groove portions are then patterned, the Cr film is etched. Since no degenerated-surface layer cannot be formed on the photoresist layer with an etchant for the Au film, the groove portions can be patterned without any degenerated-surface layer according to this method, so that high-accuracy groove portions can be formed.