A vibration generating unit with which a distal side vibration transmitting section is connected from a distal direction side, the distal side vibration transmitting section including a treatment section configured to treat a biological tissue and provided in a distal portion thereof, and the vibration generating unit being configured to generate an ultrasonic vibration having a given wavelength of the ultrasonic vibration, the ultrasonic vibration being transmitted to the distal side vibration transmitting section, the vibration generating unit comprising: an ultrasonic transducer including a piezoelectric element (32A-32D) which is configured to generate the ultrasonic vibration when an electric current is supplied thereto; a transducer attachment section to which the ultrasonic transducer is attached; a proximal side vibration transmitting section which is extended from a proximal end of the ultrasonic transducer toward a proximal direction along a longitudinal axis, and in which the ultrasonic vibration generated by the ultrasonic transducer is transmitted from the distal direction toward the proximal direction, a proximal end of the proximal side vibration transmitting section being placed at a position apart from a reference antinode position toward the proximal direction by an extending dimension (L1;L2) equal to an integral multiple of a half of said wavelength of the ultrasonic vibration, when the reference antinode position is an antinode position closest to the ultrasonic transducer among antinode positions (A2,A3;A2-A4) of the ultrasonic vibration placed on the proximal direction side with respect to the ultrasonic transducer; and an amplitude increasing section which is provided between the proximal end of the proximal side vibration transmitting section and the reference antinode position in an axis parallel direction parallel to the longitudinal axis, and which is configured to increase an amplitude of the ultrasonic vibration transmitted toward the proximal direction in the proximal side vibration transmitting section, the amplitude increasing section being placed at a node position closest to the reference antinode position among node positions (N2;N2,N3) of the ultrasonic vibration placed on the proximal direction side with respect to the reference antinode position. an ultrasonic transducer including a piezoelectric element (32A-32D) which is configured to generate the ultrasonic vibration when an electric current is supplied thereto; a transducer attachment section to which the ultrasonic transducer is attached; a proximal side vibration transmitting section which is extended from a proximal end of the ultrasonic transducer toward a proximal direction along a longitudinal axis, and in which the ultrasonic vibration generated by the ultrasonic transducer is transmitted from the distal direction toward the proximal direction, a proximal end of the proximal side vibration transmitting section being placed at a position apart from a reference antinode position toward the proximal direction by an extending dimension (L1;L2) equal to an integral multiple of a half of said wavelength of the ultrasonic vibration, when the reference antinode position is an antinode position closest to the ultrasonic transducer among antinode positions (A2,A3;A2-A4) of the ultrasonic vibration placed on the proximal direction side with respect to the ultrasonic transducer; and an amplitude increasing section which is provided between the proximal end of the proximal side vibration transmitting section and the reference antinode position in an axis parallel direction parallel to the longitudinal axis, and which is configured to increase an amplitude of the ultrasonic vibration transmitted toward the proximal direction in the proximal side vibration transmitting section, the amplitude increasing section being placed at a node position closest to the reference antinode position among node positions (N2;N2,N3) of the ultrasonic vibration placed on the proximal direction side with respect to the reference antinode position.