The object of the present invention is to accurately detect vehicles even under special conditions where vehicles go side by side, a motorcycle passes another vehicle in a traffic jam, or a shadow is cast on the road surface. The vehicle detecting system comprises a one dimension CCD camera 2 mounted above a road surface so as to provide one dimension light amount signal in the lane width direction from above the road surface and intermittent markings 6 disposed in the field of view of the one dimension CCD camera. When a vehicle 3 enters the field of view of the one dimension CCD camera 2, the modulation of one dimension light amount signal is disturbed. Therefore, a signal processing device 5 detects the vehicle on the basis of the output signal of the one dimension CCD camera 2 by checking the disturbance of modulation.
