This rotational mechanism (1) for treatment instruments comprises: an elongated member (6) and a cylindrical rotating member (8), the distal end and the proximal end of which are anchored to the elongated member (6) and a treatment instrument (3), respectively, and which converts elongational force applied to the proximal end by the elongated member (6) to rotation around the longitudinal axis of the distal end. The rotating member (8) comprises: a plurality of annular parallel parts (8a) that are disposed at intervals along the longitudinal axial direction and are substantially parallel with a direction orthogonal to the longitudinal axis a plurality of linear V-shaped peaks (8b) that are arranged between adjacent parallel parts (8a) in the circumferential direction along the parallel parts (8a) and connect adjacent parallel parts (8a) and a plurality of V-shaped valleys that are provided between adjacent V-shaped peaks (8b) with respect to the circumferential direction and that project radially inward. The plurality of V-shaped peaks (8b) are inclined in the same direction with respect to the longitudinal axis.Linvention concerne un mécanisme de rotation (1) pour instruments de traitement comprenant : un élément allongé (6) et un élément rotatif cylindrique (8), dont lextrémité distale et lextrémité proximale sont ancrées à lélément allongé (6) et un instrument de traitement (3), respectivement, et qui convertit une force dallongement appliquée à lextrémité proximale par lélément allongé (6) en rotation autour de laxe longitudinal de lextrémité distale. Lélément rotatif (8) comprend : une pluralité de parties parallèles annulaires (8a) qui sont disposées à des intervalles le long de la direction axiale longitudinale et sont sensiblement parallèles à une direction orthogonale à laxe longitudinal une pluralité de pics linéaires en forme de V (8b) qui sont agencés entre des parties parallèles adjacentes (8a) dans la direction circonférentielle le long des parties p
