A separator for power storage devices includes a synthetic resin film having minute pore portions, the separator having an air resistance of 30 sec/100 mL/16 μm or more and 100 sec/100 mL/16 μm or less, and a first scattering peak in a stretching direction measured by small-angle X-ray scattering measurement (SAXS) present in a range where a scattering vector is 0.0030 nm−1 or more and 0.0080 nm−1 or less.