A printed wiring board substrate according to an embodiment of the present invention is provided with a resin film and a metal layer that is layered on at least one surface of the resin film. The surface of the resin film on which the metal layer is layered comprises a modified layer having a composition that differs from the other parts of said resin film. The modified layer comprises a metal that differs from the main metal of the metal layer, metal ions, or a metal compound. The content of metal elements derived from the metal, the metal ions, or the metal compound in the surface of the modified layer is preferably 0.2-10 atomic%.