PURPOSE: To stabilize operation in controlling of an ignition timing of an engine by setting a large annealing coefficient for annealing of the ignition timing under a closing condition of a throttle valve compared to that in an opening condition, determining the ignition timing while annealing the set ignition timing, and thereby minimizing fluctuation of the ignition timing according to load fluctuation in an idling operation.

CONSTITUTION: An ignition timing regulated by an engine speed and an intake pressure is stored in a memory device 8 as a secondary map. A rotational speed and an intake pressure of an engine 100 are measured and input to an electronic control device 6. The electronic control device 6 calculates the ignition timing by using the secondary map stored in the memory device 8 for setting it. Annealing is performed by adapting a small annealing coefficient in the case that a signal (d) showing ON is output from an idle switch, that is, a normal operation is carried out. On the other hand, the large annealing coefficient is adapted in the case that the signal (d) showing OFF is output, that is, an idling operation is carried out. The ignition timing is thus determined by calculating an optimum value according to engine operation conditions, that is, opening/closing conditions of a throttle valve.