To smoothly control starting current of a motor in a stepless manner by a small capacity semiconductor switch.

By controlling a conduction phase angle of a semiconductor switch 71, a secondary coil 60 wound around an iron core around which a reactor coil (primary coil) 50 interposed between an AC power source 12 and a three-phase induction motor 14 is wound, as to reversely energize the reactor coil 50, is energized and de-energized to adjust impedance of the reactor coil 50. When the motor 14 becomes a steady operation state at rotational rising of the motor 14, the primary coil 50 is separated from between the power source 12 and the motor 14, and the AC power source 12 is directly connected to the motor 14. Starting current is smoothly controlled in a stepless manner by the change in the conduction phase angle of the semiconductor switch 71.