A colorless chromate coating film is formed on a bright aluminum wheel by subjecting the surface of an aluminum wheel to a cathodic electrolytic treatment in an acidic aqueous solution containing not less than 2 g/l of hexavalent chromium ions, 20 to 2,000 ppm of sulfate ions, 10 to 400 ppm of fluorine (F) as fluoride and not less than 20 ppm of zirconium ions at a pH of 0.6 to 1.7 at a current density of 0.5 to 15 A/dm.sup.2 for at least 30 seconds, thereby forming a coating film with a chromium coating amount of 50 to 250 mg/m.sup.2.