A porous film which has a crosslinked structure and, due to this structure, has excellent resistance to film breakage at high temperatures and excellent transverse-direction shape retention even at high temperatures, uses of the film are provided. The porous film comprises a crosslinked material of a resin composition containing a polyolefin. The film has a peak of shrinkage force in a transverse direction (TD) at a temperature region of the shutdown temperature or higher of the film, and the shrinkage force as measured at the peak being 80 N/cm.sup.2 or lower.