In a system for controlling a controlled variable of a rotary machine having plural-phase input terminals of the rotary machine in which plural-phase AC power is applied from an AC power applying module to the input terminals, a command-voltage setting module sets, based on a request value for the controlled variable, plural-phase AC command voltages for the plural-phase AC power as a feedforward manipulated variable. A current obtaining module obtains plural-phase AC currents flowing in the respective plural-phase input terminals of the rotary machine. An amplitude correcting module corrects the amplitude of at least one of the plural-phase AC command voltages based on the magnitudes of the plural-phase AC currents.