A sheath has improved compression resistance, maintains moderate bending rigidity, and has a reduced diameter to enable the sheath to be easily inserted into a bile duct, etc. A treatment instrument for an endoscope is provided with: a tubular sheath member (2) capable of being inserted into the channel of the endoscope； a wire (4) inserted into the sheath member (2) so as to be capable of being moved forward and backward in the longitudinal direction of the sheath member (2)； and a distal end treatment section provided at the distal end of the wire (4), the distal end treatment section being extended from and retracted into the distal end opening of the sheath member (2) by the forward and backward movement of the wire (4). The sheath member (2) is formed in a two-layer structure in which a metallic coil (6) and a resin tube (7) are overlapped radially and are affixed to each other at at least the longitudinally opposite ends thereof. The metallic coil (6) is configured so that longitudinally adjacent windings of the wire of the metallic coil (6) will have a transverse cross-sectional shape having complementary ridges and grooves, which are brought into close contact with each other. The resin tube (7) has higher bending rigidity than the metallic coil (6).L'invention concerne une gaine qui présente une meilleure résistance à la compression, qui maintient une rigidité à la flexion modérée et dont le diamètre est réduit pour permettre à la gaine d'être insérée facilement dans un conduit biliaire, etc. Un instrument de traitement pour un endoscope est pourvu : d'un élément de gaine tubulaire (2) pouvant être inséré dans le canal de l'endoscope ； un fil (4) inséré dans l'élément de gaine (2) de façon à pouvoir être déplacé vers l'avant et vers l'arrière dans la direction longitudinale de l'élément de gaine (2) ； une section de traitement d'extrémité distale située au niveau de l'extrémité distale du fil (4), la section de traitement d'extrémité distale étant étendue d
