| 摘要 |
PROBLEM TO BE SOLVED: To enable an optical box to be sufficiently hermetically sealed though the number of fixing screws is reduced. SOLUTION: A cover unit 11 is constituted of a cover member 31 covering the optical box 31, a frame member 32 which is made of synthetic resin and which supports the outside circumferential edge of the cover member 31 and an elastic member 33 made of foamed urethane and arranged between the frame member 32 and the box 13. Before the unit 11 is fitted to the box 13, the lower surface of the elastic member 33 is made to project from the lower surface of the frame member 32 somewhat. Then, the outside circumferential edge of the frame member 32 is provided with plural snap catches. The snap catches can be locked to the flange 13a of the box 13 with one operation. Besides, the elastic member 33 can be compressed between the box 13 and frame member 32 when the snap catches are locked.
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