[Problem] To provide an electrolysis method, whereby it becomes possible to produce oxidized water for sterilization/disinfection use in a neutral pH range by anodically oxidizing raw water, e.g., tap water, effectively utilizing halogen ions, e.g., chlorine ions, contained in the raw water. [Solution] A method for producing oxidized water for sterilization use which contains chlorine dioxide, said method comprising: electrolyzing tap water containing chlorine ions using a three-chamber-type electrolysis vessel, then trapping the chlorine ions dissolved in the tap water, and then electrolytically oxidizing the trapped chlorine ions on an anode electrode. The three-chamber-type electrolysis vessel is composed of an anode chamber, a cathode chamber and an intermediate chamber which is located between the anode chamber and the cathode chamber and is formed by providing partitioning membranes between the anode chamber and the cathode chamber. In the three-chamber-type electrolysis vessel, a partitioning membrane that isolates the anode chamber from the intermediate chamber is composed of a fluorine-containing cation exchange membrane and an anion exchange membrane, wherein a porous anode electrode is adhered onto the fluorine-containing cation exchange membrane in the partitioning membrane； a partitioning membrane that isolates the cathode chamber from the intermediate chamber is composed of a cation exchange membrane or an anion exchange membrane, wherein a porous cathode electrode is adhered onto the partitioning membrane； and an anion exchange resin is filled in the intermediate chamber.
