A plating method includes holding a substrate with a substrate holder while bringing a sealing member into pressure contact with a peripheral portion of the substrate to form an enclosed internal space in the substrate holder; performing a first-stage leakage test of the substrate holder by producing a vacuum in the internal space and checking whether pressure in the internal space reaches a predetermined vacuum pressure within a certain period of time; and if the substrate holder has passed the first-stage leakage test, performing a second-stage leakage test of the substrate holder by closing off the internal space after producing the vacuum therein and checking whether a change in the pressure in the internal space reaches a predetermined value within a certain period of time.