Method and apparatus for plating under constant current density

A plating apparatus comprising plating bath means for holding an electrolyte solution of uniform ionic concentration in said plating bath means, a common electrode plate, electrode support means for supporting articles to be plated and a standard or reference electrode, arranged relative to each other in said plating bath, first plating circuit means including a direct electric current source connected between said common electrode and said electrode means to be plated, said direct electric current source being able to supply a plating current of variable strength, second circuit means including constant direct current source means connected between said common electrode plate and said standard or reference electrode plate, resistance change detecting means operatively arranged to detect the change of electric resistance in the electrolyte solution between said common electrode plate and said standard or reference electrode plate in response to the change in the electric potential difference between said common electrode plate and said standard or reference electrode plate caused by the constant current which flows therethrough, and control circuit means operatively connected for regulating the plating current strength supplied by said direct electric current source in order to maintain a constant plating current density in response to the output of said detecting means.