In a synchronous rotary machine such as a synchronous motor, respective values of the number of pole pairs of the rotor and the number of stator slots are predetermined such as to enable drive currents to be passed through the stator windings which suppress specific varying electromagnetic forces that act on the rotor and produce vibration. The drive current of each phase of the motor consists of a fundamental-frequency sinusoidal waveform current having specific harmonic-frequency currents superimposed thereon, the harmonic-frequency currents having angular velocities which are appropriate, with respect to the angular variation velocities of the specific varying electromagnetic forces, for suppressing these forces.