PURPOSE: To introduce a combustion state by gradually stepping up the state toward a complete combustion state by so controlling a dust supply unit, a stoker, a damper that a flowing state of combustion gas flow becomes better combustion pattern than that at present.

CONSTITUTION: With process data as a control index a combustion pattern having thermal fluid analysis result data becoming better in a flowing state of combustion gas flow than that at present is obtained from data base while controlling a dust supply unit 4, stokers 5a-5d, dampers 7a-7d by a controller, and the unit 4, the stokers 5a-5d, the dampers 7a-7d are so controlled by the controller as to become the obtained pattern.