Polyolefin microporous membrane

A polyolefin microporous membrane formed of a polyolefin resin, as a main component, comprising 50 to 99% by mass of polypropylene and 1 to 50% by mass of propylene-±-olefin copolymer, wherein a content of the ±-olefin in the propylene-±-olefin copolymer is more than 1% by mass and 15% by mass or less.