| 摘要 |
PROBLEM TO BE SOLVED: To find an abnormality before the breakage of an optical fiber has advanced, and recover to a normal state by a simple repair by providing an inside visually observing window in order to visually observe the state of an optical fiber bundle in a flexible tube, form the outside of the flexible tube. SOLUTION: A connecting cylinder 21 to connect a curved section 3 and a flexible section 4 which constitute an insertion section flexible tube, is formed of a transparent member. Also, both side sections of the connecting cylinder 21 are bonded by inserting in the curved section 3 and the flexible section 4. however, the central section of the connecting cylinder 21, either one of the curved section 3 and the flexible section 4 is not superposed, and the section becomes an inside visualizing window A, and the state of an optical fiber bundle 12 for illumination, which is inserted in the insertion section flexible tube, can be visually observed from the outside. Therefore, when the curved section 3, e.g. is repeatedly bent in the vertical direction by operating a curving operation knob of an operation section, or the flexible section 4 is bent or twisted by a small radius of curvature, whether the optical fiber bundle 12 for illumination is smoothly moving or not, can be easily confirmed through the inside visualizing window A.
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