To prevent the ratio of vapor to condensate from fluctuating even if the amount of inflow vapor fluctuates, to safely operate a high-pressure vapor steam condenser, at the same time, to prevent the corrosion of equipment piping, to simplify configurations, and to reduce the costs of equipment.

In this control method of the high-pressure vapor steam condenser for condensing high-pressure vapor, the high-pressure vapor steam condenser is divided into a high-pressure steam condenser 12 for vapor condensation, and one 13 for condensate supercooling, vapor condensation is controlled by the high-pressure steam condenser 12 for vapor condensation, and the level and temperature of the condensate are controlled by the high-pressure steam condenser 13 for condensate supercooling.