A beam radiator for radiating a visible light beam on a road surface with a pattern determined according to a predetermined rule in order to inform others of the existence of a subject vehicle. In addition, an imaging device having an effective imaging region for generating an image of an entire subject pattern reflected on the road surface by the visible light beam from the beam radiator. The subject pattern formed by the visible light beam from the subject vehicle and the other pattern formed by the visible light or the invisible light beam from the other vehicle or an infrastructure are extracted by processing the image generated by the imaging device. Then, on the basis of the relation between the subject pattern and the other pattern, it is determined whether the subject vehicle is in a state where attention is required during running.
