Provided is a separator which shows excellent performance in electric insulation, electrolyte-holding property and ion- or electron-permeability and which can be stably manufactured. The separator is configured from a laminate non-woven fabric consisting of at least two layers, said layers including a non-woven fabric layer (layer I) that comprises a synthetic fiber having a fiber size of 0.1 μm or greater and less than 4.0 μm and a non-woven fabric layer (layer II) that comprises a thermoplastic resin fiber having a fiber size of 4.0-30.0 μm inclusive, and has a weight per area of 3.0 g/m2 or greater and less than 20.0 g/m2.