A continuous copper electroplating method wherein copper is continuously plated on a workpiece to be placed in a plating vessel accommodating a copper sulfate plating bath containing organic additives by use of a soluble or insoluble anode and a workpiece as a cathode, the method including overflowing the plating bath from the plating vessel in an lo overflow vessel under which the plating bath in the overflow vessel is returned to the plating vessel, providing an oxidative decomposition vessel, and returning a plating bath from the oxidative decomposition vessel through the overflow vessel to the plating vessel to circulate the plating bath between the plating vessel and oxidative decomposition vessel, and metallic copper is immersed in the plating bath in the oxidative decomposition vessel and exposed to air bubbling, so that decomposed/degenerated organic products formed by decomposition or degeneration produced during the copper electroplating can be oxidatively decomposed.