PURPOSE: To decrease the amt. of the impurities carried over from makeup water to a condenser and to lessen the ion burden on condensate treating devices by purifying the makeup water with these condensate treating devices in the state of allowing the condensate to bypass the condensate treating devices in a power generation plant, etc., then replenishing the condenser with this makeup water.

CONSTITUTION: A piping 2a from the condenser is connected via a valve 10 to the inlet pipe 6 of the condensing device and the inlet sides of the condensate treating devices 7... parallel connected to the inlet pipe 6 are connected via valves 12. The condensate 2 from the condenser is led out through a bypass pipe 4 and a piping 17 as the condensate 3 to a heater from the piping 2a bypassing the condensate treating devices 7. At the time of supplying the makeup water 1 into the system, holding water 1 is introduced through the inlet pipe 6 to the condensing devices 7 of which the valves 12 are opened. The water is purified in these devices and is then sent through the valves 13 to a condensate recovering pipe 8 so that the condenser is replenished with the makeup water. As a result, the concn. of the impurities in the system is lowered regardless of the replenishment of the makeup water 1 and the ion burden on the condensate treating devices 7 is lessened.