A metal-film forming apparatus includes: an anode; a resin substrate having a surface on which a conductor pattern layer that serves as a cathode is formed; a solid electrolyte membrane that contains metal ions and is between the anode and the resin substrate, the solid electrolyte membrane contacting a surface of the conductor pattern layer when a metal film is formed; a power supply; and a conductive member that is arranged contacting the conductor pattern layer when the metal film is formed, such that a negative electrode of the power supply is electrically connected to the conductor pattern layer, the conductive member being detachable from the conductor pattern layer, wherein the metal ions are reduced to deposit metal that forms the metal film on the surface of the conductor pattern layer when the voltage is applied.