To improve the operability of a navigation system by appropriately selecting possible operations of the navigation system corresponding to surrounding conditions during traveling.

A front distance sensor 2 emits a millimeter wave or laser beam toward the front side of a car body, receives a reflected echo signal from a front object, operates the distance to the end of a preceding car or relative speed from the received echo signal and outputs the operated result. A rear distance sensor 3 emits a millimeter wave or laser beam toward the rear side of the vehicle, receives a reflected echo signal from a rear object, operates the distance to the head of a following vehicle or relative speed from the received echo signal and outputs the operated result. Then, the surrounding conditions are judged while referring to all of the front condition of the vehicle, rear condition or condition of an advancing path as objects and the operation group of the navigation system is selected. A navigation control part 20 outputs signals to a display 25 and a speaker 26 and controls the navigation system by performing the desired display or notification.