A vibration generating unit includes an element unit, and the element unit includes a piezoelectric element generating an ultrasonic vibration by being supplied with electric power. A proximal-side fixing member abuts on the element unit from a proximal direction side and a distal-side fixing member abuts on the element unit from a distal direction side such that the element unit is sandwiched between the proximal-side fixing member and the distal-side fixing member in a longitudinal direction. The distal-side fixing member has a greater acoustic impedance than the proximal-side fixing member.
