PURPOSE: To stably protect a condensed water pressure and to supply condensed water to a deaerator by so outputting an addition signal to a deaerator water level control valve as to suppress a condensed water pressure change due to abrupt variation of a feed water flow rate.

CONSTITUTION: A deaerator water level signal and a deaerator set signal are input to a proportional integrator 16, which proportionally integrate a calculated deviation signal and inputs its signal to an adder 18. On the other hand, a feed water flow rate signal and a condensed water flow rate signal are input to a subtracter 17, which inputs a calculated deviation signal to the adder 18. When an abrupt load change occurs, a feed water flow rate is increased in response to a generator output. Thus, an addition signal from the adder 18 is increased, and input to a low value selector 19. Thus, a predetermined opening signal from a signal generator 20 becomes a low value to be selected, and an operation signal switches a deaerator water level control valve 4. In this manner, at the time of abruptly increasing the flow rate, abrupt closing of the valve is suppressed.