To prevent the stagnation of air bubbles at the surface to be treated of a spiral part and to supply a fresh electrolyte soln. so as to prevent the occurrence of the deficiency of a treated film thickness by immersing a member to be anodically oxidized which has the spiral part into a treating liquid and arranging a treating liquid ejection device and a means for applying outward swirling flow along the spiral part to the ejected treating liquid.

A scroll 2 as the member to be anodically oxidized which has the spiral part is immersed into the electrolyte soln. 9 housed in an electrolytic cell 8 and is used as an anode via an electrode member 17. A cathode cylinder 10 is arranged to face the scroll 2 on the bottom of this electrolytic cell 8 and the electrolyte soln. 9 is ejected via a pump 11 from an ejection port 6 disposed at its center toward the scroll 2. Further, a freely rotatably axial flow propeller 1 is arranged via a supporting cylinder 7 disposed on the outer periphery of the cathode cylinder 10 and is rotated by the ejection flow. As a result, the outward swirling flow along the lap surface and base of the scroll 2 is applied t the electrolyte 9.