This invention provides an apparatus for producing an electrode foil for use in aluminum electrolytic capacitors with which a high capacitance is obtained while the distortion of the foil and the leakage current can be controlled. At least two electrode plates as cathode are disposed in an electrolytic tank containing an electrolytic solution, and a direct current is supplied between an aluminum foil as anode and the electrode plates. Anodization is conducted continuously by turning the direction of the aluminum foil via rollers and conveying the foil between the electrode plates. During this treatment, the length and the position of the effective sections of the electrode plates are adjusted to keep the length to be at most two-thirds of the distance between an area near the surface of the electrolytic solution and the upper part of the bottom roller, so that the peak value of the anodizing current density appears not at the surface of the electrolytic solution but in the electrolytic solution.