[Problem] To prevent operational defects in the compressor of a supercharger, thereby preventing the generation of toxic substances caused by the incomplete combustion of a processing subject material remaining in a pressurized fluidized furnace. [Solution] The present invention includes: a compressed air supply termination step wherein, after the pressure in a pressurized fluidized furnace (20) has increased to an abnormal level, an auxiliary air supply flow path (121) connected to an auxiliary fuel combustion device (21), or at least one of the flow paths (91, 94, 95) connecting a combustion air supply pipe (24) and a compressor (24), is closed; and a compressed air supply initiation step wherein at least one of the flow paths (94, 96) connecting a starting burner (22) of the pressurized fluidized furnace (20) and the compressor (62) is opened.