PURPOSE: To improve power generating efficiency by intensifying negative pressure in a condenser by means of a water head given to the drainage gathered in a condenser for collecting the fluid that has driven a turbine, and driving a hydraulic turbine to generate electric power.

CONSTITUTION: The steam that was supplied to a steam turbine 6 and has completed a work is cooled to water in a condenser 9 wherein the water is utilized as cooling water therefor and the remainder is stored in a hot water well 12. The warm water (drainage) stored in the hot water well 12, after supplied with a head by, for example, a pipe, is introduced to a hydraulic turbine 13 to increase negative pressure in the condenser 9 by the water head and to drive the hydraulic turbine 13. Thus, since the drainage is utilized for driving the hydraulic turbine 13, generated energy per unit productive well is increased and therefore total power generating efficiency can be improved.