Polyolefin microporous membrane useful as separator for electricity storage device

A polyolefin microporous membrane formed of a polypropylene-based resin composition comprising 20 to 95% by mass of a polypropylene-based resin having (polypropylene)/(propylene copolymer) (mass ratio) of 90/10 to 0/100 and 5 to 80% by mass of an inorganic filler, wherein a melting point of the propylene copolymer is 110°C to 150°C, and a ratio of (propylene copolymer)/ (inorganic filler) (mass ratio) is 0.1/1 to 1.5/1.