A frequency generator comprises a cylindrical rotor to which an annular multipolar magnet is fixed on the inner wall thereof. The multipolar magnet includes a plurality of magnetizable sectors arranged in a circumferential direction thereof, and adjacent magnetizable sectors are magnetized alternately in reverse polarity. Within the rotor, two disk-shaped magnetic plates are supported fixedly with a predetermined space axially. On the peripheries of respective magnetic plates, a plurality of salient poles are formed with a predetermined pitch in a circumferential direction thereof. The salient poles of each magnetic plate respectively constitute a salient-pole line. Between the two salient-pole lines, a generating coil is wound in a circumferential direction thereof. To each first and second salient poles to be paired, the magnetizable sectors of different polarity of the multipolar magnet are faced in divergence relatively in the circumferential direction. A magnetic flux from the multipolar magnet interlinks with the generating coil by the salient poles to be paired of the two salient-pole lines. Accordingly, in the generating coil, an alternating signal of frequency corresponding to the rotation numbers of the rotor is generated. When constituting a motor, a driving coil is wound on the teeth of the magnetic plate.