A surgical instrument includes a vibrator capable of ultrasonic vibrations, a front mass portion that is connected to the vibrator so as to be capable of transmitting ultrasonic vibrations and has a first resonance frequency, and a front mass portion that is closer to the first mass portion than the first resonance frequency A front portion of the front mass portion and a proximal end surface of the treatment portion probe, and the treatment portion probe has a second resonance frequency which is higher than the first treatment portion, And a connecting portion that becomes an anti-node position when vibrating at a resonance frequency of 1.処置具は、超音波振動可能な振動子と、前記振動子と超音波振動を伝達可能に接続し、第1の共振周波数を有するフロントマス部と、前記フロントマス部の第1の共振周波数よりも高い第2の共振周波数を有する、被検体を処置するための処置部プローブと、前記フロントマス部の先端面と、前記処置部プローブの基端面と、を押圧して接続するとともに、前記第1の共振周波数で振動したときの腹位置となる接続部と、を備える。
