PURPOSE: To permit the setting of an advance command automatically in accordance with the change of the excessive feed of fuel and/or excessive reducing of the fuel and contrive the lightening of the load of an operator.

CONSTITUTION: A signal of a difference between the outlet steam temperature 6 of a reheater and a set value 8 is outputted to an adder 16 through a proportional integrator 12 as a control signal 11 while the signal 18 of sum of the control signal 11, added by the adder 16, and an opening degree correcting signal 14 from a function generator 15 is outputted to another adder 20. On the other hand, upon changing load, in which excessive feed and/or excessive reducing of fuel is effected, a difference between the flow rate 23 of fuel for a boiler and the static characteristic flow rate 25 of fuel in accordance with a generator output command 13 is obtained and the difference signal 30 is multiplied by a gain correcting signal 28 in accordance with the generator output command 13 while an obtained advance command signal 32 is outputted to the adder 20 through a switch 34 as a signal 33 as it is. Then, the regulation of opening degree of a RH gas damper 14 is effected by an opening degree command signal 21 obtained by adding the sum signal 18 to the signal 33.