To provide a spark ignition internal combustion engine capable of performing good combustion in both self ignition combustion and spark ignition combustion, also easily ensuring durability of the engine and a seal property of combustion gas.

An internal combustion engine is provided with a first/second intake valves 30 and a first/second exhaust valves 34, respectively opening/ closing a first/second intake passages 22 and a first/second exhaust passages 26 opened to a combustion chamber 18 synchronously with rotation of the engine, and a control valve 46 changing actual compression ratio of the engine by changing open/close timing of both the intake valves 30. In this constitution, the actual compression ratio at self ignition combustion time and the actual compression ratio at spark ignition operation time are made different by this control valve 46.