A multilayer insulated wire having two or more extrusion-insulating layers provided on a conductor to coat the conductor, wherein at least one layer of the insulating layers is composed of a polyethersulfone resin (i), or a resin mixture (ii) made by blending: 100 parts by weight of a resin (A) of at least one selected from polyetherimide resins and polyethersulfone resins, and 10 parts by weight or more of a resin (B) of at least one selected from polycarbonate resins, polyarylate resins, polyester resins and polyamide resins; and wherein at least one layer other than the insulating layer composed of the resin (i) or resin mixture (ii) is provided as an outer layer to the insulating layer and is composed of a polyphenylenesulfide resin. A transformer can also have the mentioned multi-layered insulated wire.