An inexpensive, productivity-enhanced single-phase AC synchronous motor in which stabilized synchronous pull-in can be carried out by suppressing generation of counter torque during a starting operation. Starting operation is performed while the energizing range of motor current is suppressed such that the energizing direction of motor current waveform lagging in a phase behind the output waveform from a detection sensor (17) is switched at at least the zero cross point of the output waveform from the sensor when the number of revolutions of a permanent magnet rotor (1) reaches a predetermined number of revolutions in the vicinity of the synchronous number of revolutions.