To reduce the floating density of the particles of remaining materials from a bottom to upward continuously by introducing auxiliary gas flow to the ring shape edge region coaxially with the core flow so that the particles of flowing layer sunk to the bottom of the ring shape edge region of a circulating fluidized bed are supplied to the core flow.

A fluidized bed reactor 1 is provided with an aerating region 2 expanding conically towards the top part and being connected to a cylindrical duct 4 for introducing process gas being processed inside the aerating region 2, lets the process gas flow forming a core flow K through the cylindrical duct 4 to the inside of the flowing layer reactor 1. The aerating region 2 forms the intake ports for the process gas as Venturi nozzles. Arranging a base part region 6 of the ring shape edge surrounding the duct 4 between the duct 4 and the wall 3 of the aerating region and inserting the base part opening nozzles 9 to the base part 6 of the ring shape edge, the auxiliary gas flow H is introduced from the output opening 9 to the inside of the flowing layers reactor 1 coaxially through the nozzles 9 in parallel with the core flow K.