The monitor device 24 displays, at the navigation display area 35b, navigation information normally displayed by the car navigation system being a road map around the own vehicle, the scheduled travel route and the location of the own vehicle on the map, and the like. As described above, the behavior display area 35a or the navigation display area 35b may be displayed as being enlarged to the entire display screen 34, and then, may be returned into two-divided displaying.