To prevent veporization of feedwater in piping in the case where the pressure of a deaerator in a steam power plant is lowered.

The steam power plant is provided with a boiler for generating steam, a steam turbine which is driven by the steam fed from the boiler, a condenser 8 to produce condensate by condensing the exhaust gas from the steam turbine, a deaerator 1 for heating and degasifying the condensate, and a water feeding system for supplying feedwater to the boiler from the deaerator 1 through a downcomer 2. The water feeding system is provided with a feedwater pump 5, a booster pump 3 disposed between the suction portion of the feedwater pump 5 and the downcomer 2, and a connecting pipe 6 for the condenser, which diverges between the discharge portion of the feedwater pump 5 and the boiler and is directed to the condenser.