A covered electric wire contains a conductor and an insulation covering which covers an outer surface of the conductor. The covered electric wire has a flat portion where a cross section of the conductor intersecting an axial direction of the covered electric wire has a flat shape which has a larger length in a width direction. The insulation covering contains, in the cross section of the flat portion, plane regions which contains, at the surface thereof: a width-directional region along the width direction; and a height-directional region intersecting the width direction. The insulation covering contains a region having a rounded shape having a radius at the junction between the width-directional region and the height-directional region, and the covered electric wire satisfies a relationship of R>t between the radius R and a thickness t of the insulation covering at the plane region. The wire harness contains the covered electric wire.