NOVELTY - The electrolysis device has air cooling type and water cooling type heat exchangers (200,300) to control the temperature of an electrolyzer (100) which includes an electrode plate (10) coated with platinum group metal oxide. The water cooling type exchanger is operated, when temperature measured by cell temperature sensor (110) is less than preset value. The operation of water cooling type exchanger is stopped, and the operation of air cooling type exchanger is started, when temperature detected by thermal storage tank temperature sensor (600) is less than preset value.    USE - Water electrolysis device.    ADVANTAGE - Since the electrode plate of the water electrolysis device is coated with platinum group metal oxide, the electric decomposition efficiency of the water electrolysis device is enhanced. The gases generated in the electrode plate is separated easily, thus the disassembly efficiency of the water electrolysis device is increased. Since the need of additional components is eliminated in the water electrolysis device, the power consumption of the water electrolysis device is reduced, and the cost of the water electrolysis device is reduced. The heat stored in the thermal storage tank is reused, thus the wastage of energy is reduced. The usage of the fuel by the water electrolysis device is reduced, thus the fuel cost reduction effect of the water electrolysis device is improved. The temperature of the electrolyzer is adjusted easily, thus the electric decomposition efficiency of water is improved. Hence, the generation of gas is increased, and the gases sticking to the electrode plate are removed easily.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the water electrolysis device. (Drawing includes non-English language text)    Electrode plate (10)    Electrolyzer (100)    Electrolytic cell temperature sensor (110)    Air cooling type heat exchanger (200)    Water cooling type heat exchanger (300)    Thermal storage tank temperature sensor (600)