PURPOSE: To obtain a cross-linked material having excellent electrical characteristics and excellent heat resistance and adhesion.

CONSTITUTION: A cross-linked material comprises the following four ethylenic copolymers of (A) an ethylenic copolymer comprising at least ethylene and glycidylalkyl methacrylate, obtained by radical polymerization under high pressure, (B) an ethylenic copolymer comprising at least ethylene and an unsaturated monocarboxylic acid, prepared by radical polymerization under high pressure, (C) an ethylenic copolymer comprising at least ethylene and an unsaturated carboxylic acid ester, obtained by saponifying and neutralizing an ethylenic copolymer prepared by radical polymerization under high pressure and (D) an ethylenic copolymer comprising at least an olefin and an unsaturated dicarboxylic acid, obtained by radical polymerization under high pressure or an ethylenic copolymer prepared by half esterifying the ethylenic copolymer.