PURPOSE: To achieve sufficient washing effect even when an aq. washing soln. is used by immersing an article to be washed in a washing soln. and applying ultrasonic waves to the article to be washed to perform ultrasonic washing and applying vibration and shaking to the article to be washed under ultrasonic washing.

CONSTITUTION: An aq. detergent soln. compensates the penetration force of a surfactant by ultrasonic waves and the oil film on the surface of an article W to be washed is vibrated to be converted to oil droplets by surface tension and the surfactant encloses oil droplets accompanied by this to activate emulsification forming micelles. The article W to be washed in a basket 97 is shaken in this state and the oil droplets bonded to the surface of the article W to be washed in an emulsion state are shaken off by physical action to be released from the surface of the article W to be washed. The adjacent articles W to be washed generate a mutual vibratory change and it is avoided that they are washed in an immobile state such that the surfaces of them are mutually bonded and the entire surface of the article W to be washed is properly subjected to ultrasonic washing.