PURPOSE: To provide an ultrasonic processing apparatus capable of protecting the ultrasonic vibrator provided to the ultrasonic processing apparatus using an acid.alkali aq. soln. and capable of efficiently and uniformly emitting ultrasonic waves to an aq. soln.

CONSTITUTION: An ultrasonic transmission tank 6 housing an ultrasonic transmission liquid 5 is provided to a treatment tank 4 housing a treatment soln. 3 of a work W through a partition wall 2 and an ultrasonic vibrator 7 is provided therein. Ultrasonic transmission liquid supply means 12, 13, 14, 15 are provided to the ultrasonic transmission tank 6 while a degassing means 16 and a cooling means 17 are provided to the ultrasonic transmission liquid supply means 14. The ultrasonic transmission liquid 5 is cooled to 5-30°C and degassed so as to reduce the amt. of dissolved oxygen to 0.5-3ppm. The partition wall 2 is a chemical-resistant synthetic resin plate. As the treatment soln. 3, an acid or alkali aq. soln. can be used and, at this time, the partition wall is a chemical- resistant synthetic resin plate.