Abstract: In one embodiment, a plant control apparatus controls a power plant. The apparatus includes a gas turbine, an exhaust heat recovery boiler to generate main steam, a first steam turbine driven by first steam, and a first valve to supply the first steam to the first steam turbine. The plant further includes a reheater to generate reheat steam, a second steam turbine driven by second steam, and second and third valves to supply the second steam to the second steam turbine. The apparatus includes an acquisition module to acquire a setting value of total output of the first and second steam turbines, and a control module to adjust the total output to the setting value by controlling opening degrees of the first, second and third valves. The control module controls the second and third valves to different opening degrees when adjusting the total output to the setting value.