To provide a gold displacement plating solution and a plating treatment technique, which can achieve uniform film thickness in the formation of a joint part that comprises a nickel layer, a palladium layer and a gold layer laminated in this order.

The gold displacement plating solution is used for forming, on a conductive layer comprising an electrically conductive metal, a joint part that comprises a nickel layer, a palladium layer and a gold layer laminated in this order. The gold displacement plating solution contains a gold cyanide salt, a complexing agent and a copper compound, the ratio of the complexing agent to the copper compound, i.e., the complexing agent/copper ions, in the gold displacement plating solution falls within the range from 1.0 to 500 by mole, and a compound formed from the complexing agent and the copper compound has a stability constant of 8.5 or more at pH of 4-6.