PURPOSE: To improve a method and device for treating high temp. process gas generated in high temp. process in a circulation type fluidized bed.

CONSTITUTION: In a circulation type fluidized bed reactor, a reactor 10 for treating the high temp. gas generated from the high temp. process is provided with a mixing chamber 12, a particle separator 16, and a return duct 18 for returning the circulating mass from the particle separator 16 to the mixing chamber 12. Then the return opening 24 of the return duct 18 is so arranged that the flow of solids entering the mixing chamber via the opening is directed substantially downwardly. The inlet 22 for the high temp. process gas is so arranged as to allow the high temp. process gas to flow into the mixing chamber 12 as a substantially upwardly directed solids flow so that the solids flow comes into contact with the gas flow.