Provided is a method for suppressing an increase in the zinc concentration of a plating solution when a zinc alloy plating member using nickel as an alloy element is manufactured using a zinc alloy plating apparatus. The plating apparatus includes: a plating tank; a first diaphragm tank having a first diaphragm; a cathode holding member; a first anode holding member; a soluble zinc-containing member held by the first anode holding member; a soluble metal-containing member containing the nickel which is the alloy element; and a second anode holding member for anode-electrolyzing the soluble metal-containing member. The first diaphragm tank is arranged in a manner that the first electrolytic solution is in contact with one surface of the first diaphragm and the plating solution is in contact with the other surface of the first diaphragm during use.