An operation section structure of a treatment instrument for endoscopic use has: a hook knife inserted into a body cavity; a wire having a distal end connected to the hook knife; a tubular flexible sheath provided to an outer periphery of the wire; a current-carrying plug having a main unit having a distal end connected to the sheath; a sliding member made of a conductive material and having a proximal end of the wire fixed thereto, the sliding member being capable of sliding on the main unit in longitudinal direction; a operation member capable of freely rotating in circumferential direction of the operation member; and attached to the sliding member; and a conductive section provided to the operation member, the conductive section being made of a conductive material providing conductivity by making contact with the sliding member. This configuration can rotate the distal end structure easily.