Here, it is preferable that the arrow of the symbol image 44, 44′ and the arrow of the symbol image 37, 37′ are displayed in different colors to be distinctively recognizable. For example, yellow or orange color series may be adopted to call attention to prior notice of the behavior for lane change in contrast to the abovementioned blue or green color series for the symbols 37, 37′. Further, the symbol image 44, 44′ can be further emphasized by displaying of that the entire thereof is brightened or a brightened portion moves frontward from the own vehicle side.