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 the blood vessel when a branch of the blood vessel is not present within a predetermined range from a position where the blood vessel is grasped, and a second mode to coagulate the blood vessel when the branch of the blood vessel is present within the predetermined range.
