PURPOSE: To selectively remove an inhibiting component without losing the available component in a chemical plating bath, by adjusting the pH of the chemical plating bath to a specific valve by H type cation exchange resin while removing an anion from the pH controlled plating bath by electrodialysis.

CONSTITUTION: An ion exchange tower 1 is packed with a cation exchange resin preliminarily regenerated to an H type by an acid. A chemical plating bath with pH of 11.5 or more in which a formic acid ion or a carbonic acid ion is accumulated is passed through the ion exchange tower 1 from a chemical copper plating tank 6 and the alkali component in the plating bath is removed to adjust the pH thereof to about 10 or less. Subsequently, the pH controlled plating bath is sent to the desalting chamber 4 of an electrodialytic cell 3 to be subjected to electrodialysis and the formic acid ion, the carbonic acid ion, a sodium ion are selectively separated and removed to the side of a concn. chamber 5. In the next step, the plating liquid from which the inhibiting component is removed is sent to the plating tank 6 and the pH thereof is returned to 12W13 by adding sodium hydroxide from an alkali agent tank 7.