Combustion control apparatus for engine

When an engine (1) operates in a low and medium load area and in a low and medium speed area, the combustion mode is established as a compression ignition combustion (S2) and when the engine (1) operates in other load and speed areas, the combustion mode is established as a spark ignition combustion (S3). Further, when the compression ignition combustion (S2) is performed, the mixture is stratified in the combustion chamber (3) and an ultra lean combustion is realized. As a result, both NOx reduction in an ultra lean condition and HC/CO reduction in an oxidation atmosphere can be obtained. On the other hand, when the spark ignition combustion (S3) is performed, a normal feedback control of the air-fuel ratio activates a three-way catalyst (29) to reduce HC, CO and NOx simultaneously.