The endoscopic treatment tool (1) according to the present invention has a longitudinal axis for the purpose of more reliably catching and discharging gallstones that have entered the stepped portion that is biased toward the boundary between the bile duct and the duodenal papilla. A sheath (2) having a lumen extending along, a basket portion (4) protruding from the lumen and having one or more elastic wires (4a), and an operation wire (5) for moving the basket portion forward and backward in the longitudinal direction of the sheath The elastic wire includes a maximum outer diameter portion where the outer diameter of the basket portion is maximum between the distal end and the proximal end of the elastic wire, and a direction perpendicular to a perpendicular line from the maximum outer diameter portion to the central axis of the basket portion. A first maximum portion that is a maximum in a direction opposite to the maximum outer diameter portion with respect to the central axis between the maximum outer diameter portion and the proximal end of the elastic wire in a side view from the side, and the maximum outer diameter portion and the first maximum At a position away from the vertical line And a second local maximum portion, the maximum outer diameter side with respect to a straight line first maximum portion is orthogonal to the perpendicular on the central axis in the front view of the basket is positioned on the opposite side. 胆管と十二指腸乳頭との境界に偏って生じた段差部分に入り込んだ胆石も、より確実に引っ掛けて排出することを目的として、本発明に係る内視鏡用処置具（１）は、長手軸に沿って延びるルーメンを有するシース（２）と、ルーメンから突出され、１以上の弾性ワイヤ（４ａ）を有するバスケット部（４）と、バスケット部をシースの長手方向に進退させる操作ワイヤ（５）とを備え、弾性ワイヤは、弾性ワイヤの先端と基端との間でバスケット部の外径が最大となる最大外径部と、最大外径部からバスケット部の中心軸への垂線に直交する方向からの側視において最大外径部と弾性ワイヤの基端との間で中心軸に対して最大外径部とは反対方向に極大となる第１極大部と、最大外径部と第１極大部との間で垂線から離れた位置で極大となる第２極大部とを有し、第１極大部がバスケットの正面視において中心軸上で垂線に直交する直線に対して最大外径部側とは反対側に位置している。
