A high-quality protective film for a dry film resist is provided. A film of a polyethylene is used as the protective film, the polyethylene being prepared by pressurizing ethylene with use of an ultra-high pressure compressor and then polymerizing the ethylene at a reaction temperature of 190.degree. to 300.degree. C. and a reaction pressure of not lower than 167 MPa in the presence of a radical polymerization initiator, or by pressuring ethylene with use of an ultra-high pressure compressor and then polymerizing the ethylene at a reaction temperature of 190.degree. to 300.degree. C. in the presence of a radical polymerization initiator while allowing a radical polymerization inhibitor to be present in the reaction system.