PURPOSE: To discriminate the crank angle reference position with one set of sensors in proximity to a magnetic disc, by providing a plurality of magnet pole missing parts to the magnetic disc and performing the crank angle reference position detection with a signal obtained with the missing part.

CONSTITUTION: With a distributor rotating shaft 2 which turns once when a crank shaft turns twice, a magnetic disc 3 magnetized with N and S poles alternately is fitted, and magnet pole missing parts 4, 5 are provided to the disc 3 corresponding to the reference position of cylinders of the engine. Further, the 1st sensor 6 and the 2nd sensor 7 are provided near the external circumference of the disc 3, and the output of the sensors 6, 7 informs the crank angle reference position of each cylinder as the position corresponding to the rotating angle unit signal.