METHOD OF FORMING OXIDE FILM, AND OXIDE FILM

PROBLEM TO BE SOLVED: To provide a method of forming an oxide film that releases slight amount of a gas under vacuum, produces no crack caused by thermal expansion, is highly scratch resistant, and does not contain alkali metal, and an oxide film formed by the method.SOLUTION: The method of forming an oxide film by subjecting aluminum or an aluminum alloy to micro-arc anodic oxidation accompanied by spark discharge, is characterized by employing, as an electrolytic solution, an alkaline solution prepared by adding at least one species selected from ammonia, hydrazine, ethanolamine and ammonium carbonate into a solution devoid of alkali metal and comprising at least one species selected from ammonium phosphate, ammonium borate, and an ammonium salt of an organic acid.