An electrolysis treatment apparatus for performing electrolytically treating a metal strip that is running in a certain direction is provided. A number of electrolysis cells continuously perform the electrolysis treatment with alternating currents in acidic electrolyte solutions. The electrolysis cells are arranged in series along the running direction of the metal strip. In each of the electrolysis cells, one electrode or two or more electrodes is/are provided. Each electrode is disposed so as to face a running path of the metal strip and applies alternating current. A soft start portion is provided at an entry region of the electrode at which the metal strip is fed in. Current density of the alternating current in the plural electrolysis cells is set so as to be the lowest in the electrolysis cell disposed furthest downstream with respect to the running direction of the metal strip. In at least one electrolysis cell except the electrolysis cell that is disposed furthest downstream. A low current density zone is provided at an exit region at which the metal strip is fed out.