Abstract: An ultrasonic oscillator device which has automatic gain control and which comprises a phase detector for detecting the phase difference between a load voltage and varying quantities indicating an operational condition of the load. The device further comprises a voltage control oscillator adapted to control an oscillating frequency through a direct current voltage corresponding to the phase difference. Further, the ultrasonic oscillator device is combined with a vibrator driven thereby and a small sized motor having a fan to forcedly cool the vibrator. The vibrator and the fan are accommodated in a housing, the size of which is made small, to produce a compact type machine.