PURPOSE: To control the pressure in a condenser based on the temperature of cooling water in a cooling water feed control device for cooling a condenser installed in a power plant.

CONSTITUTION: A condenser 1 includes a pressure detector 18 and the detected pressure thereof is inputted into a controller 19 through a line 23. Pipe lines 11, 12, 13 branched from a pipe line 7 are provided between intake pits 8, 9, and control valves 17, 14 are provided in the pipe lines 7, 11 respectively. When the pressure of the condenser 1 rises, the controller 19 causes the valve 17 to close and the valve 14 to open based on the signals from a setting device 21 and the detector 18. Cooling water cools steam at the condenser 1, whereby the cooling water is heated and returned to the pits 8, 9, so that the cooling water having been heated is fed again into the condenser 1 by pumps 2, 3, thereby causing the pressure of the condenser to rise. And, in order to change the pressure to its original pressure, a control to cause an operation in reverse sequence, as compared to the aforesaid control, is required, and hence the range of pressure change of the condenser can be made wider.