Abstract: An apparatus for effecting, on a metallic member, an electrolytic process such as descaling, electrolytic acid cleaning, passivation, electrolytic polishing, coloring or plating. The apparatus comprises a rotatable cylindrical electrode arranged to oppose the member to be processed, with a gap between them, a paste electrolyte supply device for introducing a paste electrolyte into the gap between the cylindrical electrode and the metallic member, a pad disposed on the outer peripheral surface of the cylindrical electrode and capable of retaining by impregnation the paste electrolyte supplied by the paste electrolyte supply device; an electrical power supply device for causing an electric current to flow between the cylindrical electrode and the member across the paste electrolyte; and a moving device for effecting relative movement between said metallic member and said cylindrical electrode.