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. In accordance with the kind of blood vessel grasped 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.