An energy treatment instrument includes a first grasping piece, and a second grasping piece which opens or closes relative to the first grasping piece and which grasps a blood vessel between the first grasping piece and the second grasping piece. An actuation state of the energy treatment instrument is switched between a first mode to coagulate a blood vessel of a circulatory system, and a second mode to coagulate a blood vessel of a pulmonary circulation in contrast to the first mode. in accordance with the kind of blood vessel grasped between the first grasping piece and the second grasping piece.
