PURPOSE: To promote the fuel combustion capacity of an incinerator, by providing a coarse powder separation means and a fine powder separation means to a powder separator while providing a coarse powdery stock material decomposing chamber equipped with feeders of high temp. air and fuel and a main incinerator to the incinerator.

CONSTITUTION: The coarse powdery stock material collected by a coarse powder separation part 22 passes through a preheating stock material chute 14" and subsequently distributed into coarse powder chutes 14e", 14f" by a coarse powder distributor 24. The fine powdery stock material collected by a fine powder separator 23 passes through a preheating stock material chute 14' and subsequently distributed to fine powder chutes 14a', 14b' by a fine powder distributor 14d and a part of the fine powder is mixed with the coarse powdery stock material of the coarse powder chute 14e" to be supplied to a decomposing chamber 20b. The remaining fine powdery stock material is supplied to the lower chamber 20a" of a main incinerator 20a through the fine powder chute 14f".