a variable speed pumping up generator includes a first speed control unit for outputting a rotating speed command signal for controlling a pump turbine in accordance with a power output command and outputting an excitation control signal to an ac excitation unit of the generator , and a second speed control unit for controlling , in a generation mode , an amount of ac excitation from an ac excitation unit when a rotating speed of a rotary shaft departs from a lower limit setting or an upper limit setting . the setting is set in accordance with the rotating speed generated during a normal operation .