PURPOSE: To enhance washing effect, by providing pipeline change-over valves to the outlet side lines of a cathode chamber and an anode chamber and connecting each outlet side line to a washing line having each supply line, a recirculation pump and a gas-liquid separation means.

CONSTITUTION: A water supply chamber 2 is mounted to the lower end of an electrolytic cell 1 and the body part of said cell 1 is separated into a central side and an outer peripheral side by a partition wall 3 and the outer peripheral side is set as a cathode chamber 4 while the central side as an anode chamber 5 and electrodes 6, 7 are respectively arranged to said chambers 4, 5. Both electrode chambers 4, 5 are respectively communicated not only with the water supply chamber 2 at the lower ends thereof but also with outlet side lines 8a, 9a at the upper ends thereof. Flow switches 10, 10a are provided to supply lines 8, 9 and bypass lines are respectively provided to the upstream sides of the flow switches. Solenoid valves 11, 11a receiving opening and closing control by the signals of the switches 10, 10a are provided to each bypass line.