A circulating fluidized bed gasification furnace has a combustion furnace 1, a cyclone collector 4 to which a combustion exhaust gas 3 from the combustion furnace 1 is introduced to collect a circulating medium 5, a fluidized bed gasification furnace 8 for formation of a fluidized bed 10 by introducing the circulating medium 5 collected in the cyclone collector 4 through a downcomer 7 and by supplying a gasification agent 9 from below and for gasification of a raw material 12 by supplying the same to a freeboard 11, and a circulation flow passage 14 for return of the circulating medium and unreacted char not gasified in the gasification furnace 8 to the combustion furnace 1. The downcomer 7 connected to the collector 4 has a lower end connected through a sealer 18 to the freeboard 11 in the gasification furnace 8. A raw material supply unit 20 is arranged to supply the raw material 12 to the circulating medium 5 between the sealer 18 and the freeboard 11.