PURPOSE: To maintain temperature in each section, at a preset value, by a method wherein output of a temperature-presetting device is subtracted from outputs of temperature sensors at the sections by subtracters, rotating speed- correcting signals each are generated so that outputs of the subtracters can be made equal to zero through function generators, and each rotating speed of fuel feeders is regulated.

CONSTITUTION: In a pressurized fluidized-bed boiler, outputs of temperature sensors 1, 2 at an evaporator-bed part and a superheater-bed part are delivered to a subtracter 4 for average temperature through an average-operating device 3, and a deviation from an output of a temperature-presetting device 27 is found. This deviation signal is delivered to a PI controller 10 through a PI controller 5, an adder 7 and a subtracter 8, and its output is respectively delivered to adders 25, 26 through multipliers 13, 14, as rotating speed control signals 13s, 14s of rotary feeders 02, 03. A fuel-requiring signal 6s is inputted to the adder 7, and outputs of presetting devices 11, 12 are respectively inputted to the multipliers 13, 14. On the other hand, outputs of tachometers 19, 20 for the rotary feeders 02, 03 are delivered to the subtracter 8 through the adder 9.