A stranded wire conductor includes a plurality of copper-based element wires which are twisted together, and is subjected to circular compression and then heat treatment. The copper-based element wires have a Ni-based plated layer on the surface. The stranded wire conductor preferably has a conductor cross-sectional area of 0.25 mm2 or less. An insulated wire includes the stranded wire conductor, and an insulator that coats the outer circumference of the stranded wire conductor.