PURPOSE: To efficiently perform washing and to achieve inexpensive and economical surface washing treatment without generating washing irregularity by finely vibrating an object to be washed by applying a mechanical impact thereto.

CONSTITUTION: An acid solution 2 being a heated aqueous sulfuric acid solution is supplied to a pickling tank 1 covered with a vinyl chloride sheet. Objects 3 to be treated are attached to a rack 4a to be suspended from a metal carrier bar 4 by the rack 4a and the carrier bar 4 is placed on the pickling tank 1 through a nonmetallic receiving material 4b after a degreasing process to dip the articles 3 to be treated in the acid solution 2. A vibrator 5 is attached to the end part of the carrier bar 4 and operated to transmit an impact and vibration to the carrier bar 4 to finely vibrate the objects 3 to be treated. Therefore, when the object 3 to be treated are dipped in the acid solution 2 while the vibrator 5 is operated, washing reaction is immediately started and air bubbles continuously float from the finely vibrated objects 3 to be treated to perform uniform and efficient washing.