PURPOSE: To reduce output signal fluctuation caused by gap fluctuation between a magnetic pole's end and an exciter/rotor by dividing the facing surface of a permanent magnet of a pick-up assembly, counterposed to an exciter surface, in two.

CONSTITUTION: The exciter/rotor 116 is provided with a tooth 132 forming an exciter surface 132a. A double speed sensor pick-up assembly 140 comprises electromagnetic speed sensors 136 and 138. The speed sensor 136 comprises a permanent magnet 154 containing the surface divided into two surfaces, 154a and 154b, by a ferromagnetic magnetic pale piece 152 and a slot 154c, a primary conductive coil 156 and an anti-cross-talk conductive coil 158. The speed sensor 138 has the similar configuration. Since the surface of the ferromagnetic magnetic pole piece 152 is divided into two so that each of it establishes the same relative relationship to the teeth of the exciter/rotor 116, it is hard to be affected by distance fluctuation.