The purpose of the present invention is to rotate a treatment part about a longitudinal axis of an elongated member and maintain the treatment part at an arbitrary rotational angular position. The present invention addresses this by providing a treatment tool rotation mechanism (1) including: a tubular elongated member (2)； a rotational member (4) which is supported at a distal end of the elongated member so as to be rotatable about the longitudinal axis of the elongated member and which has a treatment tool (3) fixed thereto； a tensile force converting member (5) which is disposed longitudinally along the inside of the elongated member, which has the rotational member fixed thereto at a distal end thereof, and which converts the tensile force applied by pulling a base end into rotation of the distal end about the longitudinal axis； and a rotation preventing mechanism (6) which is disposed between the elongated member and the tensile force converting member and which limits or allows relative rotation between the elongated member and the tensile force converting member about the longitudinal axis by increasing or decreasing the friction against an inner surface of the elongated member and/or an outer surface of the tensile force converting member by being operated by the base end side of the elongated member.Le but de la présente invention est de faire tourner une partie traitement autour d'un axe longitudinal d'un élément allongé et de maintenir la partie traitement à une position angulaire de rotation arbitraire. La présente invention aborde ce problème en fournissant un mécanisme de rotation d'outil de traitement (1) comprenant : un élément allongé tubulaire (2) ； un élément rotatif (4) qui est supporté au niveau d'une extrémité distale de l'élément allongé de façon à pouvoir tourner autour de l'axe longitudinal de l'élément allongé et qui a un outil de traitement (3) fixé à celui-ci ； un élément de conversion de force de traction (5) qui est disposé longitudinal
