While forming a curved piece by cutting the rigid pipe, the bending pieces together to form a recess to form a convex portion curved piece the other side provided an engaging portion which rotatably connected to the curved piece on one side more The bending pieces in the bending portion with a bending piece sets that continuously provided rotatably in, the engaging portion is simultaneously formed on the first projecting portion is formed in a curved piece on one side and the curved piece the other side by cutting that a first engaging portion formed by a first recess in which the first convex portion is slid, the second convex portion and the bending piece of the pair to be formed across the first recess bending piece the other side by cutting while the second projecting portions of the pair simultaneously formed on the side is a second engaging portion formed by a pair of second recesses to slide respectively, the bending pieces, the cut portion of the bottom of the first recess first reinforcing portions that wider the bending piece end of the lack one end, or a pair of bending pieces end at the other end from the bottom surface of the second concave portion is provided either one of the second reinforcing portion which is wider.硬質パイプを切断して湾曲駒を形成しつつ、湾曲駒一方側に凸部を形成し湾曲駒他方側に凹部を形成して湾曲駒同士を回動可能に連結する係合部を設けて複数の湾曲駒を回動自在に連設した湾曲駒組を備える湾曲部において、係合部は、切断することによって湾曲駒一方側に形成される第1凸部及び湾曲駒他方側に同時に形成される第1凸部が摺動する第1凹部によって構成される第1係合部と、切断することによって湾曲駒他方側に第1凹部を挟んで形成される一対の第2凸部及び湾曲駒一方側に同時に形成される一対の第2凸部がそれぞれ摺動する一対の第2凹部によって構成される第2係合部とを備え、湾曲駒に、第1凹部の底部の一部を切り欠き一端側の湾曲駒端を幅広にした第1補強部、又は一対の第2凹部の底面から他端側の湾曲駒端を幅広にした第2補強部のいずれか一方を設ける。
