The extending portion of the vibration transmitting unit can transmit ultrasonic vibration from the proximal end side to the distal end side. In the extending portion, the second constituent portion is provided on the distal end side from the first constituent portion. Yes. A third component provided between the first component and the second component in the extending portion is larger than a first cross-sectional area of the first component, and the second component One of the vibration antinodes has a third cross-sectional area smaller than the second cross-sectional area of the component, and the extending portion vibrates at any frequency within a predetermined frequency range, whereby the third component Located in the department.振動伝達ユニットの延設部は、基端側から先端側へ超音波振動を伝達可能であり、前記延設部では、第１の構成部より前記先端側に第２の構成部が設けられている。前記延設部において第１の構成部と第２の構成部との間に設けられる第３の構成部は、前記第１の構成部の第１の断面積より大きく、かつ、前記第２の構成部の第２の断面積より小さい第３の断面積を有し、前記延設部が所定の周波数範囲のいずれかの周波数で振動することにより、振動腹の１つが、前記第３の構成部に位置する。
