A system is provided for quickly converging the ignition timing to a desired timing when a large deviation occurs in ignition timing. The system comprises rough correcting operation for roughly correcting the ignition timing to a desired ignition timing and for producing a completion signal when the correction reaches a complete state, fine correcting operation responsive to the completion signal for finely correcting the ignition timing by a correcting quantity. When the correcting quantity becomes larger than a predetermined value, the rough correcting operation restarts, so that a large deviation of the ignition timing is quickly deviated.