The nonaqueous secondary battery according to the invention uses a separator 10 which is a composite resin film with a reinforcing material layer 11 integrally filled with polyvinylidene fluoride resin 12 or a separator 20 which is a composite resin film with a polyvinylidene fluoride resin layer 21 and a reinforcing material layer 22 stacked thereon. In this way, when the reinforcing material layer 11 is integrally filled with the polyvinylidene fluoride (PVdF) resin 12, or the reinforcing material layer 22 is stacked on the polyvinylidene fluoride (PVdF) resin layer 21, even if the polyvinylidene fluoride resin swells, its swelling is limited by the reinforcing material layer 11, 21 in the directions of width and length so that the separator 10 or 20 does not wrinkle.