A method for producing oxidized water for sterilization use which contains chlorine dioxide, comprising: electrolyzing tap water containing chlorine ions without adding halogen acid by using a three-chamber-type electrolysis vessel in which an intermediate chamber is located between an anode chamber and a cathode chamber and is formed by providing partitioning membranes (31, 32) between the anode chamber and the cathode chamber; trapping the chlorine ions dissolved in the tap water; and electrolytically oxidizing the trapped chlorine ions on a porous anode electrode; characterized in that an anion exchange membrane as partitioning membrane isolates the anode chamber from the intermediate chamber, a fluorine-containing cation exchange membrane is located between the anion exchange membrane and the porous anode electrode in the anode chamber, and the porous anode electrode is adhered onto the fluorine-containing cation exchange membrane, wherein a partitioning membrane that isolates the cathode chamber from the intermediate chamber has a cation exchange membrane or an anion exchange membrane and a porous cathode electrode is adhered onto the partitioning membrane, wherein the intermediate chamber is filled with an anion exchange resin, and wherein a planar permeable member (35, 36) is arranged to form a mixing chamber between the planar permeable member (35, 36) and the porous anode electrode, the planar permeable member (35, 36) being (i) a porous partitioning plate or a porous film made of a material selected from the group of polypropylene and polyethylene, or (ii) a non-woven fabric comprising entangled polymeric fibers made of polyethylene, polypropylene or polyethylene terephthalate, or (iii) a polytetrafluoroethylene (PTFE) non-woven fabric, that is to be placed in the anode chamber, so as to in fact divide the chamber and prevent direct supply of raw tap water to the surface of the anode electrode. electrolyzing tap water containing chlorine ions without adding halogen acid by using a three-chamber-type electrolysis vessel in which an intermediate chamber is located between an anode chamber and a cathode chamber and is formed by providing partitioning membranes (31, 32) between the anode chamber and the cathode chamber; trapping the chlorine ions dissolved in the tap water; and electrolytically oxidizing the trapped chlorine ions on a porous anode electrode; characterized in that an anion exchange membrane as partitioning membrane isolates the anode chamber from the intermediate chamber, a fluorine-containing cation exchange membrane is located between the anion exchange membrane and the porous anode electrode in the anode chamber, and the porous anode electrode is adhered onto the fluorine-containing cation exchange membrane, wherein a partitioning membrane that isolates the cathode chamber from the intermediate chamber has a cation exchange membrane or an anion exchange membrane and a porous cathode electrode is adhered onto the partitioning membrane, wherein the intermediate chamber is filled with an anion exchange resin, and wherein a planar permeable member (35, 36) is arranged to form a mixing chamber between the planar permeable member (35, 36) and the porous anode electrode, the planar permeable member (35, 36) being (i) a porous partitioning plate or a porous film made of a material selected from the group of polypropylene and polyethylene, or (ii) a non-woven fabric comprising entangled polymeric fibers made of polyethylene, polypropylene or polyethylene terephthalate, or (iii) a polytetrafluoroethylene (PTFE) non-woven fabric, (i) a porous partitioning plate or a porous film made of a material selected from the group of polypropylene and polyethylene, or (ii) a non-woven fabric comprising entangled polymeric fibers made of polyethylene, polypropylene or polyethylene terephthalate, or (iii) a polytetrafluoroethylene (PTFE) non-woven fabric,