An anodic-oxidation equipment for forming a porous layer on a substrate to be treated, including: an electrolytic bath filled with an electrolytic solution; an anode and a cathode disposed in the electrolytic solution; and a power supply for applying current between the anode and the cathode in the electrolytic solution, wherein the anode is the substrate to be treated, and the cathode is a silicon substrate having a surface on which a nitride film is formed. This provides a cathode material in anodic-oxidation for forming porous silicon by an electrochemical reaction in an HF solution, the cathode material having a resistance to electrochemical reaction in an HF solution and no metallic contamination, etc., and furthermore, being less expensive than a conventional cathode material. Furthermore, high-quality porous silicon is provided at a lower cost than has been conventional.