A bendable tube segment (410) includes annular members (210, 220, 230) and wire insertion portions (211, 221). The wire insertion portion (211) is provided on the annular member (210) to shift by a third angle θ3, which is an obtuse angle smaller than a first angle θ1, in the same direction as the first angle θ1. The wire insertion portion (221) is provided on the annular member (220) to shift by a fourth angle θ4, which is an acute angle larger than a second angle θ2, in the same direction as the second angle θ2.
