To provide a film substrate for wiring suitable for transmitting high frequency signal and capable of high density mounting.

The production process of a film substrate for wiring comprises a step for forming a conductor seed layer 3 by electroless plating on the surface of an organic substance film 1 composed of organic substance resin, a step for hot pressing the organic substance film 1 and a liquid crystal polymer film 4 composed of thermoplastic resin while sandwiching a conductor thin film, and a step for striping the organic substance film 1 from the conductor seed layer 3.