A power plant including: a steam generation device, a turbine (2, 3, 4) which is driven with stream generated by the steam generation device, a condenser which condenses the steam exhausted from the turbine, a feed water heater which heats condensate whose pressure is risen by a condensate pump, a deaerator which heats and de-aerates the condensate heated by the feed water heater, a deaerator water level control valve which controls a water level of the deaerator, an extraction system which introduces the steam extracted from the turbine into the feed water heater, and an extraction valve installed in the extraction system, characterized in that the power plant comprises: an auxiliary steam introduction system (50, 23) which introduces auxiliary steam into the feed water heater; an auxiliary steam control valve which is installed in the auxiliary steam introduction system and controls an amount of steam supplied to the feed water heater; and a control device which outputs opening command signals to the deaerator water level control valve, the extraction valve, and the auxiliary steam control valve, wherein the control device controls the extraction valve in a closing direction, controls to maintain an opening of the deaerator water level control valve, and controls the auxiliary steam control valve in an opening direction in a case where a rapid load increase request is made to the power plant. a steam generation device, a turbine (2, 3, 4) which is driven with stream generated by the steam generation device, a condenser which condenses the steam exhausted from the turbine, a feed water heater which heats condensate whose pressure is risen by a condensate pump, a deaerator which heats and de-aerates the condensate heated by the feed water heater, a deaerator water level control valve which controls a water level of the deaerator, an extraction system which introduces the steam extracted from the turbine into the feed water heater, and an extraction valve installed in the extraction system, characterized in that the power plant comprises: an auxiliary steam introduction system (50, 23) which introduces auxiliary steam into the feed water heater; an auxiliary steam control valve which is installed in the auxiliary steam introduction system and controls an amount of steam supplied to the feed water heater; and a control device which outputs opening command signals to the deaerator water level control valve, the extraction valve, and the auxiliary steam control valve, wherein the control device controls the extraction valve in a closing direction, controls to maintain an opening of the deaerator water level control valve, and controls the auxiliary steam control valve in an opening direction in a case where a rapid load increase request is made to the power plant. an auxiliary steam introduction system (50, 23) which introduces auxiliary steam into the feed water heater; an auxiliary steam control valve which is installed in the auxiliary steam introduction system and controls an amount of steam supplied to the feed water heater; and a control device which outputs opening command signals to the deaerator water level control valve, the extraction valve, and the auxiliary steam control valve, wherein the control device controls the extraction valve in a closing direction, controls to maintain an opening of the deaerator water level control valve, and controls the auxiliary steam control valve in an opening direction in a case where a rapid load increase request is made to the power plant.