A combustion variation value is detected, and a function that uses the detected combustion variation value is added to CVAR(i−1) to obtain CVAR(i); and using the resulting value, an exhaust gas recirculation amount and an ignition timing are obtained. A combustion variation is detected, and if the detected combustion variation value is equal to or greater than a predetermined value, the value of flag is set to be 1, and the exhaust gas recirculation amount and the ignition timing are reset to previous values. If the detected combustion variation value is less than the predetermined value, the value of the flag is set to be zero, and a current combustion variation manipulation correcting amount CVAR(i) is updated. If the value of flag is 1, the process is immediately terminated.