Provided is a high-voltage solid electrolytic capacitor having a rated voltage of several hundreds of volts. After an anodic oxide film layer is formed on a roughened surface of an aluminum foil by way of a first conversion treatment, a hydrated film is formed by way of boiling water immersion; the hydrated film is provided with a second conversion treatment at a formation voltage lower than that of the first conversion treatment such that an anodic foil is formed; and a conductive polymeric layer is formed on a surface of the anodic foil.