To reduce the cost and improve the leak current characteristics by anodic-oxidating an anode contg. a sintered Ta power layer in a soln. contg. monomers of conductive macromolecules and additives to form a dielectric oxide film layer and a solid electrolyte layer of conductive macromolecules at once.

An anode contg. a sintered Ta power layer is anodic-oxidated in a soln. contg. monomers of conductive macromolecules and additives to form a dielectric oxide film layer and a solid electrolyte layer of conductive macromolecules at once. The conductive macromolecule is anodic-oxidated in a soln. contg. monomers of pyrrole or thiophene at a monomer concn. of 0.2 mol or less, and the additive is a 10C or less lower alkyl sulfonate facilitating forming the dielectric oxide film layer and the solid electrolyte layer of conductive macromolecules at once on a Ta electrode. The lower alkyl sulfonate is triisopropyl Na sulfonate.