To perform emergency prevention of the excess increase of a feed water temperature at the inlet of a deaerator even when control of a deaerator inlet temperature is brought into a disorder by providing a low pressure feed water bypass pipe bypassing a low pressure feed water heater system from the outlet of a condensate pump to the inlet of a deaerator.

Feed water boosted by a condensate pump 18 is branched into a low pressure feed water heater 20 and a gas low pressure feed water heater 11 by a low pressure feed water distribution valve 28 and flows to a deaerator 21. The inlet feed water temperature of the deaerator 21 is controlled to a value lower than an upper limit value set in consideration of specified surplus for a saturated temperature corresponding to a pressure in the deaerator 21. However, when the inlet feed water temperature of the deaerator 21 is increased due to disorder of a condensate blow regulation valve 25 and control and exceeds an upper limit value, a low pressure feed water heater bypass valve 27 located in a heater bypass pipe 26 to connect together the outlet of a condensate pump 18 and the inlet of the deaerator 21 is rapidly opened. As a result, a feed water temperature at the inlet of the deaerator 21 is rapidly decreased by low temperature feed water at the outlet of the condensate pump 18.