PURPOSE: To efficiently remove chromaticity components, odorous components, etc., by allowing water to be treated to flow down from the upper to the lower part of a treating tank packed with packing materials and supplying the bubbles of ozone into the packed bed of the treating tank, thereby treating the water to be treated.

CONSTITUTION: The water 1 to be treated is allowed to flow down from the upper to the lower part like an arrow in the single treating tank 2 and is thereby treated. This water is subjected to an oxidation treatment by the ozone bubbles ejected from an air diffusion pipe 4 connected to an ozone generator 3. The packed bed constituted of packing materials 5, such as gravel, lightweight aggregate and plastic particles, extending from the bottom end to the central part is constituted in the treating tank 2. The water 1 to be treated is subjected to the filtration treatment while the water is brought into contact with the packing materials 5, by which the fine SS components are surely filtered away. The ozone bubbles ejected and supplied from the air diffusing pipe 4 are dispersed and finely segmented by coming into contact with the packing materials 5 to make the oxidation treatment of the water 1 to be treated. The chromaticity components, bromine components, COD, etc., are thereby removed.