At the first display device 3, a symbol image 61 indicating the travel course for the lane change is displayed at the front windshield 15 in addition to the symbol image 37 indicating the scheduled travel course. Similarly, at the second display device 4, a symbol image 61′ indicating the travel course for the lane change is displayed at the behavior display area 35a of the monitor device 24 in addition to the symbol image 37′ indicating the scheduled travel course. The symbol image 61, 61′ is not limited to the illustrated arrow mark and may be displayed instead of the symbol mark 37, 37′