PURPOSE: To get a motor wherein single phase AC power is used as input and rotational speed can be adjusted freely and the life is long by making the motor into such one that the switching element is turned on or turned off by detecting the angle of rotation of a rotor having becomes the specified value by a rotor position detecting circuit.

CONSTITUTION: When the contact (a) of a changeover switch 31 is turned on and a light emitting diode 26 lights, a rotor position detecting circuit 24 turns on a switching element 15, receiving the light. Hereby, the series circuit of secondary coils 8, 9, 10, and 11 and secondary coils 7, 6, 5, and 12 gets in the short circuit condition, and induced electromotive force occurs, and a current flows, whereupon torque is generated and this rotates a rotor 4. Furthermore, when the rotor 4 rotates, a rotor position detecting circuit 23 receives the light, and hereafter continues the rotation in the same manner. In case that the emit ting diode 27 is lit by changing over the changeover switch 31 to (b), the current flowing to the secondary coil becomes small, and speed falls.