(1) A flame-retardant resin composition comprising 100 to 250 parts by weight of metal hydroxide, and 5 to 50 parts by weight of acetate or 5 to 80 parts by weight of calcium carbonate based on 100 parts by weight of thermoplastic resin. (2) An insulating electric wire having a cover layer of the flame-retardant resin composition. (3) A thin high-strength insulating electric wire where a conductor having an outside diameter of 1.0 mm or less is covered with a layer of the flame-retardant resin composition having a thickness ranging from 0.1 to 1.0 mm. (4) An insulating tube and a heat-shrinkable tube formed by tubing the flame-retardant resin composition. (5) A flat cable having an insulating cover of the flame-retardant resin composition, conductors parallel arranged in the cover, and a polymer film joined to one side of the insulating cover. (6) A DC high-tension electric wire having an insulating cover of the flame-retardant resin composition. (7) An article comprising the flame-retardant resin composition cross-linked especially by irradiation with ionizing radiation. They are free from the problem of producing harmful gas when burned and excellent in mechanical strength and flame-retardance. The insulating electric wire and the flat cable are preferably applied to internal wiring of consumer electronic apparatus, vehicles, and ships.