This control apparatus of an engine includes an engine, a state quantity setting device, an injector, a spark plug, and a controller. The controller outputs a control signal to the spark plug at a predetermined ignition timing such that, after air-fuel mixture is ignited and combustion is started, unburned air-fuel mixture is combusted by autoignition, and the controller advances an ignition timing when the temperature before start of compression in a combustion chamber is to be reduced.