The treatment instrument (12) has a first treatment part (32) and a second treatment part (34). The first treatment section (32) has a first member (42) and a second member (44). By moving the first member (42) and / or the second member (44) along the longitudinal axis (L) of the sheath (22), the first contact surface (52) of the first member (42) and the first member (42) are moved. The distance between the second contact surfaces (62) of the two members (44) can be changed. When the first contact surface (52) is close to the second contact surface (62), the distal end of the rod-shaped second treatment part (34) is located closer to the distal side than the distal end of the first treatment part (32). . In this state, a high-frequency current is passed through the living tissue through the second treatment section (34), and the living tissue in contact with the second treatment section (34) is incised or peeled off (monopolar treatment). A blood vessel is sandwiched between the first contact surface (52) and the second contact surface (62), a high-frequency current is passed through the blood vessel through the first member (42) and the second member (44), and the blood vessel is coagulated and sealed. (Bipolar treatment). Thus, both treatments are possible without exchanging the treatment instrument.処置具(12)は第１処置部(32)及び第２処置部(34)を有する。第１処置部(32)は第１部材(42)及び第２部材(44)を有する。第１部材(42)及び／又は第２部材(44)をシース(22)の長手軸(L)に沿って移動することで、第１部材(42)の第１接触面(52)と第２部材(44)の第２接触面(62)の間の間隔を変更できる。第１接触面(52)が第２接触面(62)に近接しているとき、ロッド状の第２処置部(34)の先端は第１処置部(32)の先端より先端側に位置する。この状態で、第２処置部(34)を通じて生体組織に高周波電流を流し、第２処置部(34)に接触する生体組織を切開又は剥離する（モノポーラ処置）。第１接触面(52)と第２接触面(62)の間に血管を挟み、第１部材(42)及び第２部材(44)を通じて血管に高周波電流を流し、血管を凝固、封止する（バイポーラ処置）。このように、処置具を交換することなく両方の処置が可能である。
