An insulated wire that has a stranded wire conductor, and an insulator that covers an outer circumference of the stranded wire conductor. The stranded wire conductor is made up of at least a plurality of copper-based element wires twisted together, and has been heat-treated after circular compression. The copper-based element wire(s) has (have) an Ni-based plated layer on the surface. The Ni-based plated later has been compressed by the circular compression. The insulator is composed of a cross-linked ethylene-tetrafluoroethylene based copolymer, and has a heating deformation rate in the range of 65% or more, as determined under predetermined conditions using predetermined formulae in conformity with ISO6722.