The directions of optical axes of headlights of a vehicle are adjusted based on a steering angle by switching filters of different response speed characteristics. The filters are provided with hystereses along boundaries neighboring to each other. The filters are switched depending upon the steering angle and a steering angular velocity to vary the response of swivel control. Therefore, the start of swiveling is not quickened, the filter is not frequently switched, quick motion is suppressed and, hence, smooth motion is realized making it possible to execute a swivel control without causing discomfort.