Conventionally, there is known an inter-vehicular distance measuring device that takes, with an image sensor, an image of a leading vehicle travelling in front of the self-vehicle in the same direction as the self-vehicle, while the self-vehicle is travelling with the headlights on. Based on the taken image, the inter-vehicular distance between the self-vehicle and the leading vehicle is calculated. Based on the calculated inter-vehicular distance, the high/low beams of the headlights are switched, and the expansion and the light quantity of the light beams of the headlights are controlled (see, for example, patent document 1).
The inter-vehicular distance measuring device displays, on a display screen, the image of the leading vehicle (follow target vehicle) that the self-vehicle is to follow, while surrounding this image with a window. Accordingly, the driver can recognize which leading vehicle is selected as the follow target vehicle.
[Patent Document 1] Japanese Laid-open Patent Publication No. H6-84099