PURPOSE: To prolong the life of a chemical plating bath and to enhance the quality of a plating film, by replenishing a plating metal ion to the chemical plating bath by treating said chemical plating bath with a cation exchange resin having the metal ion adsorbed therewith.

CONSTITUTION: An ion exchange tower 3 is packed with a weak acidic ion exchange resin 13 which is, in turn, washed with pure water in a storage tank 7. Subsequently, sulfuric acid with a concn. of about 5% is sent to the exchange tower 3 from an acid tank 4 to convert a part of the ion exchange resin 13 to a H type while a caustic soda solution with a concn. of about 4% is sent to the exchange tower 3 from an alkali storage tank 5 to convert the same to a Na type. In the next step, the ion exchange resin 13 is washed with water and, thereafter, a copper sulfate solution with a concn. of about 16% is sent from a copper salt storage tank 6 to convert the Na type to a Cu type through the adsorption of a copper ion. After washing and backwashing are further performed, the chemical plating bath of a copper ion replenishing tank 2 is passed through the ion exchange tower 3 by a pump P-1 to elute the copper ion which is, in turn, again returned to the replenishing tank 2 to be supplied to a chemical copper plating tank 1 through a recirculation tank 10 and a filter 11 while the plating bath of the plating tank 1 is sent to the replenishing tank 2 by the pump P-1.