PURPOSE: To acquire an anodic oxide film of good characteristics as an insulating film without roughness on a surface by patterning a metallic film and by anodizing thereafter a surface of the metallic film after light etching treatment.

CONSTITUTION: A metallic film 10 of Al or Al metal, etc., is formed on a substrate 1 by sputtering method and a resist mask 11 is formed to pattern it to a configuration of a gate electrode G and its wiring part. After the resist mask 11 is peeled off and a surface of the metallic film 10 is cleaned, light etching treatment is performed for a surface of the metallic film 10. When the surface of the metallic film 10 is lightly etched using positive-type photoresist developer as etchant, residue of photoresist attaching to the surface of the metallic film 10 is completely removed by etching of the metallic film surface. After light etching treatment to the surface of the metallic film 10, the metallic film 10 is anodized from the surface as conventional and an anodic oxide film 10a is formed on the surface of the metallic film 10.