| 摘要 |
PROBLEM TO BE SOLVED: To easily set the light beam irradiation range of a scanning photo sensor according to the size of a monitoring area. SOLUTION: A slit plate 30 having a slit width D depending upon the size of an assumed monitoring area is disposed in a designated position in front of a scanning mirror 12, and the irradiation range of the scan beam BM1 from the scanning mirror 12 is limited to the slit width D. An irradiation area limiting means is constructed to change the limited irradiation range, to be concrete, provided with a plurality of slit plates different in slit width, wherein the slit plate having a slit width corresponding to an assumed irradiation range of the monitoring area is selected, and the slit plate is capable of varying the slit width corresponding to the change of the light beam irradiation range of the monitoring area. |
