PURPOSE: To enable automatic response with variation in resonance frequency due to difference of washing works by sending information on washing works together with washing command from a high-order controller and by adjusting a matching adjustment controller in accordance with this information.

CONSTITUTION: When washing works 1 placed in a washing cage are carried to an ultrasonic washing tank 2 by a transfer robot and dipped in a washing solution 3, information on works 1 such as quantity and kind is sent together with washing command from a high-order controller 4 to a matching adjustment controller 11 through a signal line 12. The controller 11 drives a servomotor 13 and turns a trimmer 14 to an angle preset by the number of works 1, thereby adjusting the oscillation frequency of a high-frequency oscillator 5 to a resonance frequency. After adjustment, the controller 11 sends high-frequency output ON command to the oscillator 5 through a signal line 15 as well as high-frequency power to a coaxial cable 8 to issue ultrasonic waves from an ultrasonic vibrator. This process can set ultrasonic output always to a maximum automatically with variation in resonance frequency due to difference of washing works 1, so that washing effect can be improved.