On a surface-roughened aluminum foil, an aluminum oxide film as an anodic oxide film is formed. Then, a conductive polymer layer as a solid electrolyte is formed thereon and thereafter a first metal plating layer is directly formed on the conductive polymer layer, thereby forming a cathode portion. On the other hand, a second metal plating layer is formed on another portion of the surface-roughened aluminum foil, which is not subjected to anodic oxidation or which is subjected to anodic oxidation followed by polishing or formation of an anode deposition film, to thereby form an anode portion. Third metal plating layers are formed at the anode and the cathode portions to obtain a capacitor element. A plurality of capacitor elements are stacked and bonded together by fusion after formation of the third metal plating layers. Alternatively, the capacitor elements may be bonded together by a conductive paste without the third metal layers.