To provide a premixed compression ignition internal combustion engine capable of surely suppressing the discharge of nitrogen oxide, hydrocarbon, and carbon monoxide.

This internal combustion engine comprises a mixture jetting injector 10 for jetting a mixture into a combustion chamber 5 and an injection timing control means 12 for so controlling injection timing for the mixture that an air-fuel ratio at the center 18 of the combustion chamber 5 is equal to a predetermined value, for example, 25 to 30. The engine further comprises a premixing chamber 11 for forming the mixture, fuel supply injectors 13, 14, and fuel supply amount control means 16, 17 for controlling the supply amount of fuel. The fuel supply amount control means 16, 17 increase the supply amount of fuel with high octane number under high load, and increase the supply amount of fuel with low octane number under low load. The engine further comprises a mixture injection control means for jetting the mixture into the combustion chamber 5 by controlling the injection timing of the mixture by the injection timing control means 12, the ratio of the supply amounts of fuel by the fuel supply amount control means 16, 17, and the premixed air amount in the premixing chamber 11 independently for each cycle.

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