To provide a water purifier capable of preventing algae from growing in a water tank.

A water purifier D1 comprises a water tank 1, a filtration tank 30, a water receiving tank 2, a filtration tank 3, a decolorization tank 10, a denitrification tank 25, a pair of electrodes 4, 4, a direct-current power supply, an electrode holder, a suction pipe, a circulation pump 7, and a return pipe 12. The iron ions eluted to a water receiving tank 2 by electrolysis react with phosphoric acid in water to produce water-insoluble phosphorus compounds, which are flocculated. A part of the flocculated water-insoluble phosphorus compounds floats on water, and the other part precipitates and accumulates in the water receiving tank 2. The denitrification tank 25 is installed on the downstream side of the decolorization tank 10, and carries out denitrification where nitrate ions or nitrite ions in water are changed to nitrogen gas by the reduction action of denitrifying bacteria (anaerobic microorganisms) in water.