A single-phase AC synchronous motor, comprising: a starting operation circuit for starting said motor as a DC brushless motor, said starting operation circuit rectifying alternate current supplied from a single-phase AC source by a bridge rectifier circuit, generating direct current smoothed by a filter circuit, and switching start-switching means (Q1-Q6) on the basis of detection signals sent from a detection sensor, which detects positions of magnetic poles of a permanent magnet rotor, so as to switch the direction of motor current and supply the motor current to a motor coil connected to the single-phase AC source; a synchronous operation circuit supplying the alternate current to the motor coil so as to perform synchronous operation as an AC synchronous motor; an operation changing switch (SW1, SW2) being provided between the single-phase AC source and the motor coil, said operation changing switch selectively energizing said starting operation circuit and said synchronous operation circuit; and control means for controlling said operation changing switch to change the energization from said starting operation circuit to said synchronous operation circuit so as to perform the synchronous operation, wherein said control means controls said operation changing switch, on the basis of the detection signals of the detection sensor, so as to perform the starting operation in a state where said operation changing switch connects the single-phase AC source to said starting operation circuit, characterized in that the starting operation is performed while the energizing range of the motor current is suppressed such that the energizing direction of a motor current waveform lagging in a phase behind an output waveform from the detection sensor is switched at at least the zero cross point of the output waveform from the sensor when number of revolutions of the permanent magnet rotor reaches a predetermined number of revolutions in the vicinity of synchronous number of revolutions, and said control means controls said operation changing switch so as to change the operation to the synchronous operation when an electric angle of phase difference between revolution phase of the magnetic poles and a source voltage waveform reaches a predetermined angle range with the start-switching means maintaining the predetermined number of revolutions of the permanent magnet rotor higher than the synchronous number of revolutions, while performing synchronous pull-in. a starting operation circuit for starting said motor as a DC brushless motor, said starting operation circuit rectifying alternate current supplied from a single-phase AC source by a bridge rectifier circuit, generating direct current smoothed by a filter circuit, and switching start-switching means (Q1-Q6) on the basis of detection signals sent from a detection sensor, which detects positions of magnetic poles of a permanent magnet rotor, so as to switch the direction of motor current and supply the motor current to a motor coil connected to the single-phase AC source; a synchronous operation circuit supplying the alternate current to the motor coil so as to perform synchronous operation as an AC synchronous motor; an operation changing switch (SW1, SW2) being provided between the single-phase AC source and the motor coil, said operation changing switch selectively energizing said starting operation circuit and said synchronous operation circuit; and control means for controlling said operation changing switch to change the energization from said starting operation circuit to said synchronous operation circuit so as to perform the synchronous operation,