PURPOSE: To automatically make the center of a headlight and the center of a light receiving device coincident and directly facing by enumerating a center position from the a part of circumference in the video of the light of the headlight with picture processing.

CONSTITUTION: The light of a lamp is caught by a CCD camera 4 in a light receiving device 3, the circumference of a video 1 is plotted and resolved into blocks, perpendicular lines 2 and 2' are disposed from both ends of a quarter circular arc 1a and a position where the dots of an intersection points are concentrated is found as a center 5 and is made directly facing automatically by moving the light receiving device 3 vertically and horizontally. Besides, in the case of a polygon or heteromorphy, from the video 18 of a concave mirror (a reflecting mirror) in the lamp, centers 19a and 19b are enumerated from a part of horizontal circular arcs 18a and 18b in the same manner and the intermediate position between both centers is determined as a lamp center position.