FIGS. 6A and 6B illustrate a display screen 34 of the monitor device 24 in an enlarged manner. The monitor device 24 is used normally as a display device of a car navigation system mounted on the automobile 14. In this case, as illustrated in FIG. 6A, the display screen 34 is occupied substantially entirely by an information display area 34a that displays map data including a variety of road information for performing route guidance of a current position and to a destination during travelling. A touch-panel type operational area 34b may be arranged along a lower edge side thereof.