In order to improve a response to a sensitivity of an accelerator pedal of a motor vehicle and a sudden acceleration of the vehicle, width of an insensitive zone provided in a vicinity of a portion of a first logic pattern for auto-cruise control, in which portion a difference of accelerator opening is zero, is made very narrow or a second logic pattern having substantially no insensitive zone is provided, which is selected under a specific condition such as when the vehicle runs on an ascending road.