Even when the gripping piece is largely swung, the base end of the gripping piece does not have to protrude in the radial direction of the support portion, and for the purpose of reducing interference with surroundings, the medical treatment tool ( 1) A long support portion (2) and a tip end of the support portion (2), at least one of which is swingably supported around a swing axis (A) orthogonal to the longitudinal axis of the support portion (2). A pair of gripping pieces (3, 4), and a driving mechanism (5) for swinging the gripping piece (4). The driving mechanism (5) is provided at a base end of the gripping piece (3). A cylindrical portion (8) having a central axis about the oscillation axis (A), and a cylindrical portion (8) is rotatably supported inside the cylindrical portion (8) around an axis parallel to the oscillation axis (A). A driving member (7) having an outer surface that is brought into rolling contact with the inner surface, and transmitting the power applied at the base end of the support portion (2) to rotate the driving member (7). And a power transmission member (6).把持片が大きく揺動させられても把持片の基端部を支持部の径方向に突出させずに済み、周囲との干渉を低減することを目的として、本発明に係る医療用処置具（１）は、長尺の支持部（２）と、支持部（２）の先端に、支持部（２）の長手軸に直交する揺動軸線（Ａ）回りに少なくとも一方が揺動可能に支持された一対の把持片（３，４）と、把持片（４）を揺動させる駆動機構（５）とを備え、駆動機構（５）が、把持片（３）の基端に設けられ、揺動軸線（Ａ）を中心軸とする円筒部（８）と、円筒部（８）の内側に揺動軸線（Ａ）と平行な軸線回りに回転可能に支持され、円筒部（８）の内面と転がり接触させられる外面を有する駆動部材（７）と、支持部（２）の基端において加えられた動力を伝達して駆動部材（７）を回転させる動力伝達部材（６）とを備える。
