PURPOSE: To optimize the driving of a soot blower, by a method wherein the characteristics of a boiler in the limit of contamination of the heat transfer surfaces thereof are compared with actually measured values as the deciding data for the driving of the soot blower.

CONSTITUTION: The temperature of combustion gas is detected by a temperature detector T6 in a flue 5 and the detected data is inputted into the analog input circuit 10 of a control unit 8. Test data or operated values of relations between the temperature of combustion gas at the position of the temperature detector T6 and the condition of contamination of the heat transfer surface of a heat exchanger are memorized previously into the memory 12 of the control unit 8 with respect to each load of a boiler as the deciding data of the limit of contamination of the heat transfer surfaces of the boiler. The deciding data are compared with the actually measured data of the temperature detector T6 by a CPU 9 to determine the operation of a soot blower. When the conditions of the soot blower are different with each other, the blowing of several times are effected with respect to a test sequence so as to memorize a plurality of operation systems previously while the temperature of the combustion gas is measured in each time whereby the optimum sequence is selected statistically.