PURPOSE:To provide the subject device wherein a control gain is switched by a signal starting the opening of a recirculation valve to compensate the rapid variation of the blow quantity gain, thereby to smoothly carry out the control of the quantity of feed water to a boiler below the recirculation quantity. CONSTITUTION:A gsin adjustor 25 is switched by a signal change-over apparatus 26. In the case where a recirculation valve 5 is closed, a feed water pump turbine speed setting signal 12 is supplied as it is to a feed water pump turbine speed setting apparatus 111, whereas, in the case where the recirculation valve 5 is opened, the feed water pump turbine speed setting signal 12 is switched so as to pass through a gain adjustor 25 by a change-over signal imparted by the opening signal detector 27 of the recirculation valve 5. A suitable gain lowering quantity is preset in the gain adjustot 25, and when the recirculation valve 5 is closed, the gain adjustor 25 is restored to the original condition.
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