The bending tube segment (410) includes an annular member (210, 220, 230) and wire insertion portions (211 and 221). The wire insertion portion (211) is disposed on the annular member (210) while being shifted in the same direction as the first angle θ1 by a third angle θ3 that is an obtuse angle smaller than the first angle θ1. The wire insertion portion (221) is disposed on the annular member (220) with a fourth angle θ4 that is an acute angle larger than the second angle θ2 in the same direction as the second angle θ2.湾曲管セグメント（４１０）は、環状部材（２１０，２２０，２３０）と、ワイヤ挿通部（２１１，２２１）とを有する。ワイヤ挿通部（２１１）は、第１角度θ１と同じ方向に第１角度θ１よりも小さい鈍角である第３角度θ３ずらして環状部材（２１０）に配設される。ワイヤ挿通部（２２１）は、第２角度θ２と同じ方向に第２角度θ２よりも大きい鋭角である第４角度θ４ずらして環状部材（２２０）に配設される。
