PURPOSE: To suppress a discharge amount of aldehyde into the atmosphere at the time of inaction of a catalyst in a catalytic device, in the case that the catalytic device is provided in an exhaust passage by using alcohol mixed fuel.

CONSTITUTION: At inactive time of a catalyst (S1, S2) with alcohol concentration in a predetermined value or more(S3) further with an exhaust temperature at 400 to 500°C (S5), ignition timing is corrected advanced and delayed (S7, S8).