One jointed member 42 composed of a copper plate is inserted in a quean acid soluble 38 of an electrolytic treatment part 30 to be used as a cathode, so as to reduce an oxidation film by the electrolytic treatment. 電解処理部30のクエン酸溶液38に銅板からなる一方の被接合部材42を挿入して陰極とし、電解処理によって酸化膜を薄くする。 - 特許庁