A vibration generating unit includes a proximal side vibration transmitting section in which an ultrasonic vibration is transmitted from a distal side toward a proximal side. A proximal end of the proximal side vibration transmitting section is placed at a position apart from a reference antinode position toward the proximal direction by an extending dimension equal to an integral multiple of a half wavelength, when the reference antinode position is the closest to the ultrasonic transducer among antinode positions placed on the proximal direction side with respect to the ultrasonic transducer. The vibration generating unit includes an amplitude increasing section increasing an amplitude of the ultrasonic vibration transmitted toward the proximal side in the proximal side vibration transmitting section.