Separator for Electric Power Storage Device, and Electric Power Storage Device in which Same is Used

Provided are: a separator for an electric power storage device, the separator having high liquid absorption and high strength; and an electric power storage device in which the separator is used. The separator for an electric power storage device includes a microporous membrane (A) containing an inorganic filler and a polyolefin resin. The microporous membrane (A) has a MFR of 0.05-5 inclusive, includes not less than 20 mass % but less than 100 mass % of the organic filler, has an average pore diameter of 100-1500 nm inclusive for the pores in a cross-section ND-MD, and has an air permeability of 340 sec/100 mL or less.