A conventional synchronous motor may not have a motor control circuit board, and stator windings of the motor are directly powered by an AC power supply, so that the stator generates an alternating magnetic field, and the permanent magnet rotor is oscillated. If the rotor obtains enough kinetic energy, the oscillation amplitude of the rotor will continue to increase. Finally, the rotation of the rotor is quickly accelerated to synchronize with the alternating magnetic field of the stator. Due to the characteristics of the alternating current and the stop position of the permanent magnet rotor is not fixed, it is not guaranteed that the rotor rotates in the same direction every time it starts. In the prior art, the motor control circuit board can be set to control the energization of the stator winding according to the position of the magnetic pole of the rotor and the polarity of the AC power supply, so as to ensure that the rotor can rotate in the same direction each time the rotor is energized.