PURPOSE: To detect PG accurately even if the energy of magnetic material goes high.

CONSTITUTION: 1 is a disclike magnet fixed to the rotary shaft of a motor, and it is magnetized in eight magnetic poles from N1 to S8 being equally divided excluding Nj and S2 which are slid by Δθ from the equal division lines. A detection element, which has a two-line section, is provided on stator side, and if magnets rotate, in the equal division area, the two lines of the detection element become the same magnetic poles and the output is zero, but when N1 and S2 being slid by Δθ cross the detection element, an output signal is gotten, and based on this, a PG signal can be gotten.