A vibrating body unit includes a vibration generator, a vibration transmitter and first amplitude enlarger. The vibration generator generates ultrasonic vibration whose amplitude has a predetermined correlation with a frequency. The vibration transmitter has a proximal end and a distal end while the vibration generator is attached from a proximal side, and transmits the ultrasonic vibration to a distal side in a longitudinal axis direction. At least one first amplitude enlarger is provided in the vibration transmitter, and enlarges the amplitude of the ultrasonic vibration at a first amplitude enlargement rate in a direction of transmission of the ultrasonic vibration, the first amplitude enlargement rate having a correlation with the frequency opposite to the predetermined correlation.
