The bending mechanism (3) comprises a plurality of curved joint members (4) connected in series so as to swing mutually about a swing axis (S), a plurality of curved joint members (4) connected to each curved joint member A pair of elongated tension transmission members (6) and a plurality of flexible sheath members (7) bundling the tension transmission members (6) of each pair so as to be relatively movable in the longitudinal direction, wherein each sheath The member (7) has a branch position (S) located closer to the distal end side than the swing axis (S) located directly on the proximal end side of the curved joint member (4) to which each tension transmission member (6) , A pair of tension transmission members (6) are bundled and a pair of tension transmission members (6) separated from each other on the distal end side of the branching position are connected to different positions of the curved joint member (4).湾曲機構(3)は、揺動軸線(S)回りに相互に揺動可能に直列に連結された複数の湾曲関節部材(4)と、各湾曲関節部材(4)に一対ずつ接続された複数対の長尺の張力伝達部材(6)と、各対の張力伝達部材(6)を長手方向に相対移動可能に束ねる可撓性を有する複数本のシース部材(7)とを備え、各シース部材(7)は、各対の張力伝達部材(6)が接続されている湾曲関節部材(4)の直基端側に位置する揺動軸線(S)よりも先端側に配置された分岐位置まで一対の張力伝達部材(6)を束ね、分岐位置よりも先端側において互いに分離した一対の張力伝達部材(6)が、湾曲関節部材(4)の異なる位置に接続されている。
