PURPOSE: To prevent over advancing of the ignition timing due to overshoot, by employing such an arrangement that the ignition timing is calculated on the basis of a correction value of the quantity of intake air drawn per one rotation of an engine in case that overshoot is caused with an air flow sensor.

CONSTITUTION: In order to detect occurrence of overshoot, comparison is made between a correction value P and the quantity Q/N of intake air drawn per one rotation of an engine. In case that no overshoot is caused with an air flow sensor, the value Q/N is used directly at a step 70. However, if overshoot is caused with the air flow sensor, the correction value P is used at a step 69. The ignition timing is calculated by use of the values N and Q/N corrected in the above-mentioned manner, whereby it is enabled to prevent faulty control of the ignition timing due to overshoot.