A condensate flow rate control device for a power plant, which is adapted to a power plant having: a boiler; a steam turbine (14,16,18) configured such that steam generated by the boiler is introduced thereinto; a generator configured to be driven by the steam turbine (14,16,18); a condenser configured such that exhaust hot steam from the steam turbine (14,16,18) is supplied thereto; a deaerator configured such that condensate generated by the condenser is supplied thereinto via a deaerator water level adjustment valve and such that bleed steam from the steam turbine (14,16,18) is introduced thereinto; and a feed pump which is configured to supply feedwater deaerated by the deaerator to the boiler, wherein the condensate flow rate control device comprises a water level adjustment unit configured to perform condensate flow rate control, configured such that a frequency fluctuation or a requested load change is inputted thereinto, and configured to adjust pressure in a condensate flow path extending from the deaerator water level adjustment valve to the deaerator so that the inputted frequency fluctuation is suppressed or an output value of the generator conforms to the inputted requested load change, thereby adjusting an amount of bleed steam from the steam turbine (14,16,18), characterized in that the water level adjustment unit is configured to calculate, based on a preset relationship between a frequency fluctuation or a requested load change and a water level or a holding water amount of the deaerator, a setting value of the water level or a setting value of the holding water amount from the frequency fluctuation or the requested load change and to output an opening instruction to the deaerator water level adjustment valve so that the water level or the holding water amount of the deaerator assumes the setting value of the water level or the setting value of the holding water amount. a boiler; a steam turbine (14,16,18) configured such that steam generated by the boiler is introduced thereinto; a generator configured to be driven by the steam turbine (14,16,18); a condenser configured such that exhaust hot steam from the steam turbine (14,16,18) is supplied thereto; a deaerator configured such that condensate generated by the condenser is supplied thereinto via a deaerator water level adjustment valve and such that bleed steam from the steam turbine (14,16,18) is introduced thereinto; and a feed pump which is configured to supply feedwater deaerated by the deaerator to the boiler, wherein the condensate flow rate control device comprises a water level adjustment unit configured to perform condensate flow rate control, configured such that a frequency fluctuation or a requested load change is inputted thereinto, and configured to adjust pressure in a condensate flow path extending from the deaerator water level adjustment valve to the deaerator so that the inputted frequency fluctuation is suppressed or an output value of the generator conforms to the inputted requested load change, thereby adjusting an amount of bleed steam from the steam turbine (14,16,18), characterized in that the water level adjustment unit is configured to calculate, based on a preset relationship between a frequency fluctuation or a requested load change and a water level or a holding water amount of the deaerator, a setting value of the water level or a setting value of the holding water amount from the frequency fluctuation or the requested load change and to output an opening instruction to the deaerator water level adjustment valve so that the water level or the holding water amount of the deaerator assumes the setting value of the water level or the setting value of the holding water amount.