PURPOSE: To simplify a fuzzy inference for finding a timing advance, leading to the simplification of an execution circuit for this fuzzy inference, as well as to shorten a span of the required time for the fuzzy inference.

CONSTITUTION: A timing advance is determined according to a knocking compensation timing advance found out by an fuzzy inference from the compensation timing advance found out by the fuzzy inference from a fundamental timing advance determined out of engine speed and opening of a throttle valve or the like and knocking information, while ignition timing determined out of a crank angle by the timing advance is compensated, finding the compensated ignition timing, and an ignition control signal is generated at the compensated ignition timing is given to an igniter. With this constitution, the fuzzy inference for finding the timing advance is simplifiable, leading to the simplification of an execution circuit for the fuzzy inference, thus the required time for the fuzzy inference is reducible.