To provide a method and device for accelerated oxidation treatment, by which a high removal rate of organic substances can be obtained with a reduced amount of ozone and by which ozone can be used efficiently even when the organic substance content in water varies.

This accelerated oxidation treatment device is provided with an oxidation reaction means for oxidizing the organic substances having a reactor filled with the water and a fine bubble generating means for dissolving ozone in the water, an ion removing means, a TOC concentration measuring part, an ozone concentration measuring part, and an oxidation reaction control means which controls the ozone concentration measuring part and/or the TOC concentration measuring part, and at the same time, controls the circulation of the water based on the inputted measurement results so that untreated, water is mixed with the water from the reactor or the ion removing means.