The treatment instrument 2 includes a first jaw 8 having a first gripping surface, a second jaw 9 having a second gripping surface for gripping a living tissue between the first gripping surface, and a first jaw provided on the first gripping surface. A first electrode 10, a second electrode 11 provided on one of the first gripping surface and the second gripping surface, to which high-frequency power is supplied between the first electrode 10, and the first gripping surface and the second gripping surface Between the first electrode 10 and the second electrode 11 when viewed along the facing direction with the first gripping surface and the second gripping surface facing each other. And a floating electrode 12 to be disposed.処置具２は、第１把持面を有する第１ジョー８と、第１把持面との間で生体組織を把持する第２把持面を有する第２ジョー９と、第１把持面に設けられる第１電極１０と、第１把持面と第２把持面との一方に設けられ、第１電極１０との間に高周波電力が供給される第２電極１１と、第１把持面と第２把持面との少なくとも一方に設けられ、第１把持面と第２把持面とを互いに対向させた状態で当該対向する方向に沿って見た場合に、第１電極１０と第２電極１１との間に配置されるフローティング電極１２とを備える。
