A cathode (102), by applying a voltage between the card (42) which will form the anode, copper on the card is etched. The cathode (102) and the card (42) is immersed in the electrolyte, the electrolyte, the first state of forming ions having metal atom having an oxidation number of the first positive, than the first oxidation number including small second positive second to state it is reduced or at least a first forming an ion containing a metal atom having an oxidation number of components. The first redox potential of the electrolyte for reduction from the first state to the second state, from the second oxidation-reduction potential of the electrolytic solution for reducing divalent copper ions to metallic copper large. During the etching, while the first component is reduced from a first state to a second state, metallic copper on the card is oxidized, are converted to positively charged copper ions. Since the metal of the copper is not precipitated on the cathode, thereby improving the quality of the etched structure on the card.