PURPOSE: To obtain a rotating magnetic field of three times of an input power source and to enable high speed rotation, by a method wherein an AC motor and a magnetic frequency multiplier obtaining two-phase output are integrated.

CONSTITUTION: A magnetic triple frequency multiplier is constituted by two pairs of magnetic poles of 12 and 13, yokes 1, 2, 3, 4, and windings 5, 6, 7, 8, 9, 10. Triple frequency magnetic flux waveform passes through a rotor 11 and a rotating magnetic field is produced, whereby the rotor 11 is rotated at the synchronous speed of triple frequency. A capacitor is connected to windings 14, 15, and a resonance circuit to increase triple magnetic flux is formed. In this constitution, an AC motor can be rotated at high speed without necessitating a frequency convertor such as an inverter.