Spark ignition internal combustion engine

A spark ignition type internal combustion engine comprising a variable compression ratio mechanism able to change a mechanical compression ratio and a variable valve timing mechanism able to control a closing timing of an intake valve, wherein an actual compression ratio and ignition timing in a predetermined standard state after completion of engine warm-up are stored in advance as a reference actual compression ratio and a reference ignition timing in accordance with each operating state of the engine, when a temperature which represents an engine temperature is lower than a temperature in the standard state or when an intake air temperature is lower than an intake air temperature in the standard state, if at the time of engine high speed operation, the actual compression ratio is made to increase over the reference actual compression ratio so as to make a thermal efficiency rise, while if at the time of engine low speed operation, the ignition timing is made to advance over the reference ignition timing so as to make the thermal efficiency rise.