PURPOSE: To contrive a stable control by invalidating the total unit correction, existing till that time, and performing the new total unit correction when a partial correction amount exceeds a predetermined reference value in accordance with an engine speed, in the case of the ignition timing characteristics performing its total unit correction and partial correction.

CONSTITUTION: An ignition timing arithmetic device 20, being based on an engine speed calculated in an arithmetic part 22 and an intake air amount calculated in an arithmetic part 23, calculates a basic fuel injection width in an arithmetic part 24. While an arithmetic part 25 calculates the basic ignition timing being based on the engine speed and the basic fuel injection width. Further an arithmetic part 26 calculates a total unit correction coefficient being based on a knocking signal from a knocking decision circuit 12. While an arithmetic part 27, being based on the knocking signal, calculates a partial correction value in every lattice divided by the engine speed and the basic fuel injection width. And when the partial correction value exceeds a predetermined reference value in accordance with the engine speed, and arithmetic part 28 decides arithmetic execution of the new total unit correction value.