To provide a compact device for removing nitrogen and phosphorus components contained in waste water.

The nitrogen component in the waste water is converted into nitrogen oxides or ammonia by electrolysis of the waste water and also these are transferred into electrolytic production gas from the waste water and then the nitrogen component is removed. Also, by the electrolysis using the electrodes 1, 2 made of iron and aluminum, the nitrogen and the phosphorus components are simultaneously removed. Besides, the water after the treatment is transmitted thorough a reverse osmosis membrane, then the nitrogen and phosphorus components are removed with high removal efficiency.