The treatment instrument has a longitudinal axis, a lumen through which a guide wire can be inserted is formed along the longitudinal axis, a first opening that is open in communication with the distal end side of the lumen, and a proximal end of the lumen A sheath having a second opening that is communicated on the side and opened to the outer peripheral surface, a proximal end holding portion that holds a proximal end region at the proximal end portion of the sheath, and a distal end region of the proximal end portion of the sheath A distal end holding portion that is connected to the distal end of the proximal end holding portion at an angle at which the second opening is located on the extension of the central axis of the lumen in the distal end region and is deflected with respect to the proximal end holding portion. And comprising.処置具は、長手軸を有し、長手軸に沿ってガイドワイヤを挿通可能なルーメンが形成されるとともに、ルーメンの先端側で連通して開口された第一の開口部と、ルーメンの基端側で連通して外周面に開口された第二の開口部とを有するシースと、シースの基端部における基端領域を保持する基端保持部と、シースの基端部の先端領域を曲げて保持し、先端領域におけるルーメンの中心軸の延長上に第二の開口部が位置する角度で基端保持部の先端と連なって基端保持部に対して偏向して設けられた先端保持部と、を備える。
