To provide an insulating film capable of retaining thickness at thermal crimping and of maintaining superior insulating characteristics by this.

For polyolefin 1, the insulating film having an insulating layer 3 in which cross-linked polymer particulates 2 which are not plastically deformed at the melting point of the polyolefin 1 are dispersed is used. As the cross-linked polymer particulates, one kind or a plurality of kinds of particulates selected from a group composed of cross-linked polyacrylic acid ester, cross-linked polymethacrylic acid ester, and cross-linked polystyrene can be used. In the insulating film, on one or both uppermost surfaces of the insulating film, an adhesive layer or a sealant layer composed of acid-modified polyolefin resin can be laminated. The insulating film is most suitable for the insulating film to be used for a battery pack.