Abstract: An internal combustion engine comprising a combustion chamber, an injection chamber connected thereto through an injection port, a secondary inlet passage opening to the injection chamber, and a secondary inlet valve for opening and closing the secondary inlet passage. A spark plug is extended into the combustion chamber so as to dispose a spark gap of the plug close to the injection port. At the suction stroke of the engine, air in the injection chamber is injected near to the spark gap through the injection port to blow away the combustion gas around the gap and also to generate a strong swirl and turbulence of the mixture in the combustion chamber, thereby improving firing and combustion of the lean mixture in the combustion chamber to reduce the discharge of noxious components in the exhaust gas and improve the fuel consumption.