An octane rating estimating section estimates the octane rating of fuel on the basis of detection signals from intake air temperature, water temperature, fuel and knock sensors. A pre-ignition occurrence index calculating section calculates a pre-ignition occurrence index on the basis of the estimated octane rating; and a pre-ignition occurrence index correcting section corrects the pre-ignition occurrence index such that pre-ignition occurs more easily. An automatic idling stopping determining section determines automatic idling stopping on the basis of a determination result of an automatic idling stopping prohibition determining section which determines the prohibition of automatic idling stopping on the basis of the pre-ignition occurrence index, an operation signal from the air conditioner, and steering information; and a fuel injection control section which controls fuel injection per the automatic idling stopping determination result.