The attention-calling mark 49, 49′, 49″ is displayed for calling attention of an occupant based on that the following vehicle 48 is recognized as a vehicle rapidly approaching the own vehicle from the rear. Accordingly, it is preferable that the attention mark 49, 49′, 49″ is displayed in a striking color such as red and orange. Here, it is also possible to vary the color in accordance with a distance between the own vehicle and the following vehicle 48. For example, the color may vary from yellow to orange and to red in accordance with decrease of the distance between the own vehicle and the following vehicle 48. Further, it is possible to call more attention of an occupant by blinking the attention-calling mark 49, 49′, 49″.