To easily practice stratification and make it easy to stratify burnt gas inside a combustion chamber.

A controlled self ignition combustion method of a four stroke engine containing a plurality of cylinders 1 respectively including at least a first intake means 2 and at least a first exhaust means 5 (common pipe) transfers exhaust gas from the cylinder in the exhaust phase to another cylinder in the exhaust phase through at least one specific ports 4 of respective cylinders during partial load operation.