Abstract: A surgical operation device comprising an ultrasonic piezoelectric transducer for generating ultrasonic vibrations, an oscillation feedback type oscillator for supplying high-frequency power to the ultrasonic transducer, a vibration transmitter connected to the ultrasonic transducer for transmitting and amplifying mechanical vibrations at an ultrasonic frequency, a suction unit and an irrigator. The ultrasonic transducer includes a bolted Langevin type transducer. The feedback circuit of the oscillation feedback type oscillator includes an oscillation voltage detector, a phase comparator, a low pass filter, a differential amplifier, and a voltage controlled oscillator. Thus, the mechanical resonant frequency can be traced in a wide range of fluctuations of a load on the vibration transmitter during vibration and vibrations can start an appropriate mechanical resonate frequency irrespective of the load status of the vibration transmitter at the start-up.