| 摘要 |
PURPOSE:To project laser light on a light receiving window readily, by providing a means, by which the light receiving window part of a light receiving part is lighted brightly so that the window part can be recognized in the darkness. CONSTITUTION:A lamp 22 is provided between a sheet of ground glass 21, which is provided at a light receiving window 5a of a light receiving part 5, and a sensor part 5b. At this time, the light from the lamp 22 is projected only on the side of the light receiving window 5a. An index plate 23, on which a scale is printed, is provided between the lamp 22 and the ground glass 21. The central position of the light receiving part observed from the input side of the laser light can be displayed by the scale. In this constitution, the light receiving window 5a is lighted brightly and be readily recognized visually even in the darkness in the tunnel. When the scale is displayed, the index of the input point of the laser light is obtained and this is very convenient. |
