Problem to be solved: to provide a welding structure of an inner tube which can obtain a junction structure between tubes welded by back wave welding without lowering junction strength.First conduitA small diameter portion forming a part of the communicating conduit connected to the second conduitExtending from the center of the small diameter portion to the central axis of the first pipe；Large diameter portion with inner diameter larger than inner diameter of small diameterHaving a stepped portion formed at the end of the large diameter portion and the opposite endThe second conduitThe tube connection is smaller than the inner diameter of the large diameter portion.The length of the second tube in the central axis direction has a tube connection which is longer than the insertion length to the first conduitThe opposing region is opposed to the stepped portion and the tube connection.In the case where the end portion on the opening side of the large diameter portion is non containing,A laser beam is applied to the region around the entire circumference of the first tubeA weld portion welded back to the inner peripheral surface of the second tube is formed in the thickness direction of the first pipe from the outer surface of the first pipe.Diagram【課題】接合強度が低下することなく裏波溶接された管同士の接合構造を得ることができる内視鏡管路の溶接構造を提供すること。【解決手段】第一の管路は、第二の管路に連なって連通管路の一部を形成する小径部と、小径部の間口から当該第一の管路の中心軸方向に延設し、内径が小径部の内径よりも大きい大径部と、大径部の間口と反対側の端部に形成される段部とを有し、第二の管路は、外径が大径部の内径よりも小さい管路接続部であって、当該第二の管路の中心軸方向における長さが第一の管路への挿入長よりも長い管路接続部を有し、段部と管路接続部とが対向する対向領域を含み、かつ大径部の開口側の端部が非含有の領域であって、第一の管路の周方向の全周に亘る領域にレーザ光を照射して、第一の管路の外表面から第一の管路の厚さ方向に第二の管路の内周面まで裏波溶接された溶接部が形成される。【選択図】図４
