An object of the invention is to provide a method for producing a laminated film comprising at least two resin films bonded together, which is capable of increasing the adhesiveness of the bonding surface and forming a laminated film with high reliability. The method for producing a laminated film according to the invention comprising at least two resin films laminated together, which comprises: a fluorination treatment step comprising bringing a fluorine and oxygen atoms-containing treatment gas into contact with at least a partial region of the surface of at least one of the two resin films to increase the adhesiveness of the region; and a bonding step comprising bonding the two resin films together using, as a bonding surface, the surface that has been brought into contact with the treatment gas.