PROBLEM TO BE SOLVED: To provide a compact device which continuously and efficiently generates active oxygen.
SOLUTION: In a composite electrode, cathodes 1b carry a redox polymer which can produce active oxygen and spacers 1c of 0.005 to 5 mm thickness which transmit or permeate a liquid are present between anodes 1a and cathodes 1b. By bringing the composite electrode into contact with a liquid, the redox polymer reduces oxygen dissolved in the liquid to produce active oxygen, while the oxidized redox polymer is reduced by accepting electrons from the cathodes. Thus, active oxygen is continuously generated. As for the redox polymer, polyaniline is preferably used.