PURPOSE: To dissolve oxygen in water free of residual ozone by blowing ozone into water to form the bubble, irradiating the bubble with UV to convert ozone to singlet oxygen and then irradiating the bubble with visible light, etc., to convert the singlet oxygen to ground-state oxygen.

CONSTITUTION: The air contg. ozone is introduced from an air pipe 3 into a purification cylinder 1 being supplied with raw water from an inlet 2 and diffused from a pipe 4 as the ozone bubble 5, the bubble 5 is floated up along with raw water. The bubble is successively passed through the UV lamp 6 emitting an UV of 254nm wavelength, for example, halogen lamp 8 emitting a visible light of 600-65nm wavelength, for example, and halogen lamp 9 emitting a near IR of 1200nm wavelength, for example, set above the diffuser pipe 4 to generate a singlet oxygen molecule and a singlet oxygen atom in the ozone. The singlet oxygen molecule is converted to the ground-state oxygen molecule and the singlet oxygen atom to the ground-state oxygen atom and dissolved in the raw water.