PURPOSE: To efficiently heat an intake system by setting the ignition timing of only one cylinder to an overlapping period of opening intake-exhaust valves and shifting the overlapping ignition timing sequentially to the other cylinders to return all cylinders to an ordinary ignition timing after warming up.

CONSTITUTION: In a multicylinder engine in which alcohol fuel is injected to an intake port, any one of multicylinders, for example only a first cylinder, has the ignition timing of a ignition plug set to an overlapping period d of opening intake and exhaust valves. Then, the remaining cylinders are set to ordinary ignition timing A. Also, the overlapping ignition period B of intake and exhaust valves is advanced about 360°C of crank angle for example before the ordinary ignition timing A. And the overlapping ignition timing is shifted sequentially from the original cylinder to the others one by one. Then, one cylinder for example the first one having the original overlapping ignition timing returns to the ordinary ignition timing.