PURPOSE: To improve the accuracy of controlling ignition timing by detecting a position between crank angle signals which are generated at every certain crank angle, using clock pulses.

CONSTITUTION: A high-frequency clock signal K being used in a mircocomputer 2 is applied to a programmable timer 3. During the time between the generation of a unit angle signal θB' and the generation of the next unit angle signal θB', a crank angle is detected by counting the number of clock signals K, to control ignition timing. Thereby, the accuracy of controlling the ignition timing can be improved without need for improving the accuracy of the unit angle signal.