| 摘要 |
<p>PURPOSE:To prevent the quantity of light entering a light reception element from decreasing extremely even if a vehicle passes below a land bridge by setting the directional angle of the light reception element to an obtuse angle. CONSTITUTION:A holder 3 is provided on the upper surface of a case 2 for storing a light reception element. The holder 3 causes a plate 4 to be engaged so that the plate 4 can slide freely. The case 2 is provided with a first edge 22 at an opening 21. The plate 4 is provided with a second edge 41. The area of a window W surrounded by the first edge 22 and the second edge 41 corresponds to the slide position of the plate 4. The first edge 22 and the second edge 41 nearly form V shape. The plate 4 is provided with a knob 42 for sliding the plate 4 itself.</p> |
