PURPOSE: To detect PG signals using a simple constitution wherein no projection or magnet for a PG is separately provided.

CONSTITUTION: Part of a magnet 21 for a field system is magnetized into a PG magnet 2 having areas of the polarity opposite to that of the field magnet 21. A PG pattern 24 for detecting magnetic field variation signals through the PG magnet 23, is formed on a stator base 13. The PG pattern 24 is formed by connecting a first through fourth patterns 24a-24d together. When the first and second patterns 24a, 24b are opposed to the areas of the opposite polarity of the PG magnet 23, the third and fourth patterns 24c, 24d are opposed to the areas of the opposite polarity of the field magnet 21. Then a current passes through the patterns 24a-24d in the same direction, and that current is detected as a PG signal.