The treatment instrument (10) includes a first gripping member (124), a second gripping member (174) configured to open and close with respect to the first gripping member (124), and a heat dissipation member (112). And a first heat conducting member (132). In a process in which the first gripping member (124) and the second gripping member (174) change from the closed state to the open state, the predetermined position between the closed state and the open state is switched. The position is a first area from the closed state to the switching position, and the second area is from the switching position to the opened position. The first heat conducting member (132) thermally disconnects the first holding member (124) and the heat radiating member (112) in the first region, and the first region in the second region. The holding member (124) and the heat dissipation member (112) are thermally connected. 処置具（１０）は、第１の把持部材（１２４）と、第１の把持部材（１２４）に対して開閉するように構成された第２の把持部材（１７４）と、放熱部材（１１２）と、第１の熱伝導部材（１３２）とを備える。第１の把持部材（１２４）と第２の把持部材（１７４）とが閉じた状態から開いた状態へと変化する過程において、閉じた状態と開いた状態との間の所定の位置を切替わり位置とし、閉じた状態から切替わり位置までを第１の領域とし、切替わり位置から開いた状態までを第２の領域とする。第１の熱伝導部材（１３２）は、第１の領域においては第１の把持部材（１２４）と放熱部材（１１２）とを熱的に非接続状態とし、第２の領域においては第１の把持部材（１２４）と放熱部材（１１２）とを熱的に接続状態とする。
