A medical treatment tool of the present invention includes a supporting unit； a pair of grasping pieces, at least one of which is supported on the supporting unit so that the at least one grasping piece pivots on a pivot axis orthogonal to a longitudinal axis of the supporting unit； and a driving mechanism causes the grasping piece to pivot. The driving mechanism includes a cylindrical part disposed at a proximal end of the grasping piece and having the pivot axis； a driving member having an outer surface that makes rolling contact with an inner surface of the cylindrical part, the driving member being rotatably supported on an inner side of the cylindrical part so that the driving member rotates about an axis parallel to the pivot axis； and a force transmitting member transmitting a force applied to a proximal end of the supporting unit to rotate the driving member.
