An optical axis control assembly is provided with a plurality of control means which are supplied with information necessary for deciding the tilt angle of the car body 1, and determine the body tilt angle by sharing the input information with the other control means; and optical axis control means for controlling the optical axis of each headlight based on the determined body tilt angle. By the combined use of a plurality of low-cost, small control devices of the same specifications each of which is incapable of determining the body tilt angle by itself because of a lack of information, the optical axis control device assembly exerts the function of determining the body tilt angle, and effects the optical axis control of the headlights based on the determined body tilt angle.