A spark ignition internal combustion engine in which, during an idling operation, the ignition timing is changed temporarily to the advance side or retard size with respect to the reference ignition timing so that when the engine speed deviates from the target idling speed, the engine speed becomes the target idling speed. When the actual compression ratio at the time of idling is changed, the reference ignition timing at the time of idling is made to move until the ignition timing at which the same generated torque of the engine is obtained.