Abstract: An anodizing method of the present invention is characterized in that in a state in which an outer peripheral surface of an aluminum pipe 2 for a photoconductor drum substrate is in contact with an electrolysis solution, a high-frequency voltage of 5 kHz or higher is applied to the electrolysis solution to conduct electrolysis to thereby form an anodic oxide film on the outer peripheral surface of the aluminum pipe 2. With this method, an anodic oxide film can be formed on the surface of the pipe, and an aluminum pipe free from burr-shaped convex defects can be produced. Furthermore, the anodizing for forming an anodic oxide film can be carried out at a higher rate, and an anodic oxide film with less electrolyte elution can be formed.