To perform the premixing compressive combustion of an internal combustion engine without knocking even under high load condition.

A premixed air-fuel mixture is compressed and self-ignited in a low load area. The lean air-fuel mixture which is not self-ignited by compression by a piston is formed in a partial area of a combustion chamber in a high load area, and the air-fuel mixture slightly thicker than the lean air-fuel mixture is formed in a remaining area. The slightly thicker air-fuel mixture is ignited, and the lean air-fuel mixture is compressed and self-ignited by the increase of pressure by the combustion of the air-fuel mixture. Whereby the air-fuel mixture in the combustion chamber can be prevented from being unexpectedly self-ignited, and the lean air-fuel mixture can be self-ignited at a proper time by controlling a time when the lightly thicker air-fuel mixture is ignited.

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