To provide an arrangement for carrying out ozone decomposition treatment of organic water which can sufficiently feed ozone and make the organic waste sufficiently react with ozone.

The organic water containing an organic substance and water is fed by an organic water feed pump 3 through an organic water feed pipe 10, and discharged to a treatment chamber 35. Ozone-containing gas containing ozone as a composition gas is fed to the treatment chamber 35 by an ozone-containing gas supply apparatus 4 through an ozone-containing gas feed pipe 21. The organic water is subjected to ozone decomposition treatment in contact with the ozone-containing gas and the organic water in the treatment chamber 35 with the treatment chamber 35 kept at a predetermined high pressure. The tip end part of the organic water feed pipe 10 is positioned on the top part of the treatment chamber 35. Spray means 12 for spraying the organic water is installed on the tip end part of the organic water feed pipe 10. While spraying the organic water by the spray means 12, the organic water is come into contact with the ozone-containing gas.