PURPOSE: To operate a soot blower with fewer number of measurement, by detecting the change of draft loss of respective members when the boiler load is high, and detecting draft loss at the boiler furnace outlet and at heat transfer pipe outlet positioned farthermost downstream of the exhaust gas stream when the load is low.

CONSTITUTION: Pressure detectors 14W20 detect the pressures on the outlet side of a group of heat transfer pipes to detect the draft loss at each heat transfer pipe. Temperature detectors 21W26 are arranged in the group of the heat transfer pipes to detect the temperature of steam or water. When the boiler load is lowered to a certain value or below, a control box 27 detects by a load signal L the difference of the detected results of the pressure detectors 14 and 20 to find the heat transfer pipe group to which dust has deposited, and dispatches a command signal to a soot blower arranged in the heat transfer pipe group to remove the dust. When the load is high, the soot blowers are controlled by respective pressure detectors. Thus, the soot blower can be efficiently operated with the objects to be measured being less in number.