ction thereof, it is better not to greatly move the optical axis of projection light.FIG. 5 is a flowchart showing an example of control when turning is detected.According to this embodiment of the invention, Steps S1 S3 are identical with the respective Steps S1 S3 of FIG. 4.When |VL.times.(VR-VL)| is judged to be greater than the threshold .alpha. at Step S3, Step S4 is followed and the directio