PURPOSE: To carry out the detoxification of PCB surely and easily at reduced cost, by heating a specific granular catalyst acting as an oxidative decomposition catalyst forming a metal oxide, at a temperature above the dissociation temperature of PCB, thereby accelerating the evaporation, thermal decomposition and combustion of PCB.

CONSTITUTION: A porous natural mineral containing various kinds of metal elements capable of forming metal oxides with heat and acting as an oxidative decomposition catalyst, or a natural or artificial mineral such as pumice stone impregnated with a solution of a salt which forms a metallic oxide with heat, is used as granular catalyst 6. The furnace 1 containing the layer of the granular catalyst 6 is preheated at a temperature above the decomposition point of PCB. PCB is passed upward through the gap between the catalyst granules 6 to effect successive evaporation, thermal decomposition and combustion at a temperature above the decomposition point of PCB. The above reactions are accelerated by the catalytic action of the granular catalyst 6. The generated chlorine gas is made completely harmless by the adsorption and neutralization in the chlorine gas-treatment system 13 connected to the furnace 1 through the line 12.