To make it possible to continuously treat a dioxin-containing gas by guiding an adsorbent adsorbing dioxins into a hydrothermal oxidation decomposition reaction device and oxidation-decomposing both the adsorbed dioxins and the adsorbent, in a device which performs the oxidation/decomposition treatment of the adsorbent adsorbing the dioxins.

In a fluidized bed adsorption column 1 which forms a fluidized bed with an adsorbent and a dioxin-containing gas, the dioxin-containing gas is adsorbed continuously. In this case, the adsorbent is continuously supplied by an adsorbent supply means 3 and a part of the adsorbent adsorbing the dioxins is continuously guided out of an adsorbent removing means 23 and a filter 24. In addition, the adsorption column 1 is combined with an upper disposed tank 2 for circulation/separation, and the adsorbent is circulated from the upper disposed tank 2 for circulation/separation into the adsorption column 1 by a circulation means 21. The dioxins separated by the adsorbent guided out of the removing means 23 and the filter 24 is oxidation-treated by an oxidation treatment device 4 together with the adsorbent.