A first conductive polymer solution in which fine particles of a conductive polymer are dispersed is applied to a dielectric layer of aluminum oxide, and this solution is dried to form a first conductive polymer layer. Next, a coating solution is applied to the first conductive polymer layer, this solution containing at least one selected from an aromatic sulfonic acid having, in one molecule of the acid, a carboxyl group and a hydroxyl group, or two carboxyl groups, and a salt of the aromatic sulfonic acid. The solution is then dried to form a coating layer. Next, a second conductive polymer solution is applied to the coating layer, the solution being a solution in which fine particles of a conductive polymer are dispersed. This solution is then dried to form a second conductive polymer layer. This process gives a solid electrolyte layer of a capacitor element.