PROBLEM TO BE SOLVED: To provide a joint mechanism that can be curved with a small towing force, and thereby achieving miniaturization of a device and improvement in control characteristics.SOLUTION: A joint mechanism 12a includes: a cylindrical first member 13a having a through-hole 17； a second member 13b disposed in the tip side of the first member 13a, and swingably provided around a swinging axis line intersecting a central axis to the first member 13a； flexible cylindrical guide sheaths 21a, 21b penetrating through the vicinity of the central axis of the through-hole 17, and having the tip fixed to the second member 13b； operation wire 22a, 22b introduced into the tip sides of the guide sheaths 21a, 21b； and folded parts 20a, 20b provided in the position eccentric in a radial direction from the swinging axis line in the second member 13b, and making a U-turn of the operation wire 22a, 22b introduced from the side of the first member 13a via the guide sheaths 21a, 21b to the side of the first member 13a. The tips of the operation wire 22a, 22b making the U-turn in the folded parts 20a, 20b are fixed in the radial-direction eccentric position.【課題】小さい牽引力で湾曲可能とし、装置の小型化および制御特性の向上を図る。【解決手段】貫通孔１７を有する筒状の第１の部材１３ａと、その先端側に配置され、第１の部材１３ａに対して中心軸に交差する揺動軸線回りに揺動可能に設けられた第２の部材１３ｂと、貫通孔１７の中心軸近傍を貫通し、先端が第２の部材１３ｂに固定された可撓性を有する筒状のガイドシース２１ａ，２１ｂと、その先端側に導入された操作ワイヤ２２ａ，２２ｂと、第２の部材１３ｂに揺動軸線から径方向に偏心した位置に設けられ、ガイドシース２１ａ，２１ｂを経由して第１の部材１３ａ側から導入されてきた操作ワイヤ２２ａ，２２ｂを第１の部材１３ａ側にＵターンさせる折り返し部２０ａ，２０ｂとを備え、折り返し部２０ａ，２０ｂにおいてＵターンさせられた操作ワイヤ２２ａ，２２ｂの先端が、径方向に偏心した位置に固定されている関節機構１２ａを提供する。【選択図】図4
