To provide an ultrasonic washer having a function of automatically detecting vibrator deterioration without adjusting the changeover of a switch and a movable contact of variable resistance even when proceeding voltage of high frequency voltage is changed.

An ultrasonic washer is constituted of a device body 11 to which washing liquid is fed, a vibrator 24 fitted to a vibration plate installed in the device body, an ultrasonic oscillator 31 electrically connected to the vibrator 24 for driving the vibrator 24 to generate ultrasonic vibration, an impedance matching circuit 33 installed between the ultrasonic oscillator 31 and the vibrator 24 for matching them, an injected voltage measuring means 44 for measuring voltage injected to the vibrator 24 and voltage reflected from the vibrator 24, a divider part 51 for dividing the voltage injected to the vibrator 24 by the voltage reflected from the vibrator 24, and an indicator part 53 for indicating the division results of the division made in the divider part.