PURPOSE: To accurately measure a cam shaft stopping position without contact by providing means for judging whether the stopping position is normal or not by noncontact type cam shaft stopping position detecting means and data processing.

CONSTITUTION: An expecting stop position index ring 2 having an expecting stopping position indicator 3 for indicating a reference position on the cam shaft of a cam shaft controller is provided, and a CCD image sensor 4 for detecting the expecting stopping position indicator 3 is provided. When a signal 12 rises after a start signal 14 is inputted, a counter 93 starts counting a pulse applied through a signal line 11. Latch circuits 91, 92 latch the starting and finishing counted values of the indicator 3. A circulating memory 90 inputs data of the latch circuits 91, 92 and a cam shaft controller. It decides whether the cam shaft stopping position is normal or not on the basis of the data.