A film forming method for a metal film comprising: placing a substrate which is a cathode on a placing table; causing a metal solution containing metal ions to be in a state of being disposed between an anode and a solid electrolyte membrane, causing the metal solution to be in a state of being sealed in a first accommodation chamber of a housing with the solid electrolyte membrane so as to cause the metal solution to be disposed on a surface (Ba) of the substrate via the solid electrolyte membrane, causing a fluid to be in a state of being sealed in a second accommodation chamber of the placing table with a thin film so as to cause the fluid to be disposed on a rear surface (Bb) of the substrate positioned on a side opposite to the surface (Ba) on which the metal film is formed, via the thin film having flexibility, and causing the substrate to be interposed between the solid electrolyte membrane and the thin film by moving the placing table and the housing relative to each other in a state in which the substrate is placed on the placing table; pressing the solid electrolyte membrane and the thin film against the substrate interposed between the solid electrolyte membrane and the thin film to cause the solid electrolyte membrane to conform to the surface (Ba) of the substrate and to cause the thin film to conform to the rear surface (Bb) of the substrate; and applying a voltage between the anode and the substrate in a state in which the solid electrolyte membrane is brought into contact with the surface (Ba) of the substrate placed on the placing table to reduce the metal ions contained in the solid electrolyte membrane and cause a metal derived from the metal ions to deposit on the surface (Ba) of the substrate so as to form the metal film on the surface (Ba) of the substrate. placing a substrate which is a cathode on a placing table; causing a metal solution containing metal ions to be in a state of being disposed between an anode and a solid electrolyte membrane, causing the metal solution to be in a state of being sealed in a first accommodation chamber of a housing with the solid electrolyte membrane so as to cause the metal solution to be disposed on a surface (Ba) of the substrate via the solid electrolyte membrane, causing a fluid to be in a state of being sealed in a second accommodation chamber of the placing table with a thin film so as to cause the fluid to be disposed on a rear surface (Bb) of the substrate positioned on a side opposite to the surface (Ba) on which the metal film is formed, via the thin film having flexibility, and causing the substrate to be interposed between the solid electrolyte membrane and the thin film by moving the placing table and the housing relative to each other in a state in which the substrate is placed on the placing table; pressing the solid electrolyte membrane and the thin film against the substrate interposed between the solid electrolyte membrane and the thin film to cause the solid electrolyte membrane to conform to the surface (Ba) of the substrate and to cause the thin film to conform to the rear surface (Bb) of the substrate; and applying a voltage between the anode and the substrate in a state in which the solid electrolyte membrane is brought into contact with the surface (Ba) of the substrate placed on the placing table to reduce the metal ions contained in the solid electrolyte membrane and cause a metal derived from the metal ions to deposit on the surface (Ba) of the substrate so as to form the metal film on the surface (Ba) of the substrate.