Some of the pieces of divisional electronic information formed by dividing an electronic control program for an automobile are stored in an automobile operating key, the rest being stored in a car-mounted storage unit, and the pieces of divisional electronic information read in from the operating key and the pieces of divisional electronic information read out of the car-mounted storage unit are united by an electronic information integration restoration device to restore the electronic control program, whereby the automobile is driven. An automobile electronic control device of high safety which prevents the driving of the automobile unless a genuine key is used by utilizing a digital control system, a key mechanism using the same and methods thereof are provided.