The treatment instrument includes a treatment section, a cover that covers the back surface of the treatment section, a cover that is disposed between the treatment section and the cover, and that, in response to an increase in temperature of the back surface of the treatment section accompanying the addition of energy, Wherein the distance between the treatment portion and the cover is increased so as to enlarge the air layer region between the treatment portion and the cover, and in response to a decrease in the temperature of the back surface, And an adjuster that adjusts so that the air layer region is contracted by bringing the distance between them close to each other.処置具は、処置部と、前記処置部の裏面を覆うカバーと、前記処置部と前記カバーとの間に配置され、エネルギの付加に伴う前記処置部の前記裏面の温度の上昇に応じて前記処置部と前記カバーとの間の距離を離隔させて前記処置部と前記カバーとの間の空気層領域を拡大し、前記裏面の温度が低下するのに応じて前記処置部と前記カバーとの間の距離を近接させて空気層領域を縮小するように調整する調整部とを有する処置体を備えている。
