Provided is a cannula (3) provided with: a first cylindrical member (21) having a tubular shape with a first longitudinal axis； a second cylindrical member (22) having a tubular shape with a second longitudinal axis； a connection mechanism (25) for connecting the first cylindrical member and the second cylindrical member in series； and a rear bearing (33) for supporting the second cylindrical member to be able to three-dimensionally swing about an axis crossing the second longitudinal axis. The first cylindrical member has a first through hole into which a flexible, thin, elongate medical treatment instrument (1) can be inserted, and is supported by a trocar attached to a body wall of a patient while being inserted through the trocar. The second cylindrical member has a second through hole into which the medical treatment instrument can be inserted. The connection mechanism connects the first cylindrical member and the second cylindrical member to be able to swing about an axis perpendicular to a plane including the first longitudinal axis and the second longitudinal axis.L'invention concerne une canule (3) pourvue : d'un premier élément cylindrique (21) ayant une forme tubulaire avec un premier axe longitudinal ； d'un second élément cylindrique (22) ayant une forme tubulaire avec un second axe longitudinal ； d'un mécanisme de liaison (25) pour relier le premier élément cylindrique et le second élément cylindrique en série ； et un palier arrière (33) pour supporter le second élément cylindrique de façon à pouvoir osciller en trois dimensions autour d'un axe croisant le second axe longitudinal. Le premier élément cylindrique a un premier trou traversant dans lequel un instrument de traitement médical allongé, mince, flexible (1) peut être inséré, et est supporté par un trocart fixé à une paroi corporelle d'un patient tout en étant inséré à travers le trocart. Le second élément cylindrique comporte un second trou traversant dans lequel l'instrument de traitement médic
