Provided is a method for forming a metal film using a solid-state electrolyte membrane, and the method allows a metal film having a smooth surface to be formed and an additive to sufficiently serve its function. A method for forming a metal film includes the successive steps of (a) supplying a solution to a solution-housing space, the solution containing ions of the metal and an additive; (b) increasing a pressure of the solution in the solution-housing space in a state where the solution-housing space is uncommunicated with a solution tank and the substrate held by a holder is in contact with the solid-state electrolyte membrane; (c) decreasing the pressure of the solution in the solution-housing space; and (d) forming the film of the metal on the substrate by applying a voltage between an anode and the substrate while the solution is circulated between the solution-housing space and the solution tank.