PURPOSE: To perform a charge and a discharge with a high current density without reducing the discharge capacity by coating a solution dissolved or dispersed with an electroactive polymer material on the surface of a current collector substrate, drying it, and forming it into a thin layer shape.

CONSTITUTION: A polymer material used as an electrode active material is electroactive and has the function to reversibly absorb or desorb ions in an electrolyte or a solid electrolyte, e.g., polyaniline. To form such an electroactive polymer material on a current collector substrate as an active material, first the polymer material is dissolved or dispersed in a proper solvent to obtain a solution. This solution is coated and dried on the surface of the current collector substrate, the polymer material is fixed into a very thin layer shape on the surface of the current collector substrate. The current density can be thereby increased to the practicable level without hardly reducing the discharge capacity.