An anodizing method in which a workpiece made of aluminum or aluminum alloy is immersed in an electrolytic solution, and treatment is performed in which the application of positive voltage for a very short period of time and the removal of charges are repeated alternately between the workpiece and a cathode arranged in the electrolytic solution includes a step of performing treatment in which the positive voltage application and the charge removal are repeated in a tentative cycle, measuring the control point arrival time of a current waveform at the positive voltage application period, and determining normal positive voltage application time based on the control point arrival time; and a step of performing treatment in which the application of positive voltage and the removal of charges are repeated in a cycle corresponding to the normal positive voltage application time, and forming an anodized film on the surface of the workpiece.