PURPOSE: To realize a NOx reduction in time of lean combustion as well as to enlarge an air-fuel ratio control range in time of this lean combustion as improving the extent of engine power at the high load, in a lean-burn engine controlling it to an output air-fuel ratio of more slightly rich than the theoretical air-fuel ratio at the high load.

CONSTITUTION: A crank angle position, where pressure in a cylinder comes to the maximum, is detected, and ignition timing is compensated so as to make this crank angle position cane nearer to a desired position θpmax. Here, whether a target air-fuel ratio is a lean air-fuel ratio or an output air-fuel ratio is judged (S22). When it is the output air-fuel ratio, another desired position θpmax1 (in and around ATDC15°), where heat efficiency canes to the maximum is set up (S23), and when it is the lean air-fuel ratio, a desired position θpmax2 that is tarier than the above-mention desired position θpmax1 and reduces the extent of NOx is set up (S24).