A grasping treatment instrument includes a first grasping piece, and a second grasping piece opening or closing relative to the first grasping piece by rotating relative to a base member. The second grasping piece includes a supported portion supported by a distal portion of the base member and forming a rotational axis of the second grasping piece relative to the base member, and a ring portion in which the supported portion is formed and which is formed in a ring shape continuous over an entire circumference around a longitudinal axis of the base member. A driving force, rotating the second grasping piece relative to the base member, is transmitted from the movable member to the ring portion.
