| 摘要 |
PROBLEM TO BE SOLVED: To more highly accurately guide light.SOLUTION: A holding structure for a folding mirror 17 includes projections 2d, 2e, and 2f positioning the folding mirror 17 to a position on a holding plane and a holding member 21 pressing the folding mirror 17 to a side part 2a from the opposite side of the holding plane across the folding mirror 17, to hold the folding mirror 17. Weights 31 and 32 are provided in the folding mirror 17 and the centroid G4 of the composite body of the folding mirror 17 and the weights 31 and 32 is located on the side nearer the holding plane S than the centroid G1 of the folding mirror 17 before the weights 31 and 32 are provided. |
