A water treatment apparatus for decomposing and removing organic substances in water to be treated includes: a hydrogen peroxide source for storing hydrogen peroxide which is added to the water to be treated; an ultraviolet oxidation device for irradiating ultraviolet light to the water to be treated to which hydrogen peroxide has been added; and a hydrogen peroxide removal device for removing hydrogen peroxide contained in the outlet water from the ultraviolet oxidation device. The hydrogen peroxide removal device includes: an anode and a cathode; and a hydrogen peroxide removal chamber disposed between the anode and the cathode and provided with a metal catalyst with ability of decomposing hydrogen peroxide. A DC current is applied between the anode and cathode.