A solid electrolytic capacitor includes a valve metal formed with an anodized film; an inner conductive polymer film formed on the anodized film; and an outer conductive polymer film formed on the inner conductive polymer film. The outer conductive polymer film is obtained by: preparing a first polymer solution (PEDOT/PSSA); dissolving a predetermined dissolved substance in a non-aqueous solvent, the predetermined dissolved substance being selected from the group consisting of boric acid, 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, 1,3,6-naphthalenetrisulfonic acid, and polystyrenesulfonic acid, and a salt thereof; mixing the dissolved solvent with pure water to obtain an additive solution; adding the additive solution into the first polymer solution to obtain a second polymer solution; and applying the second polymer solution to the inner conductive polymer film.