Coated electric wire and lead wire harness

Provided are: a covered electric wire which is capable of obtaining high flame retardancy in a structure in which an insulating coating is provided on the outer periphery of a conductor having a flat cross-section; and a conductive wire harness which is provided with such a covered electric wire. Provided is a coated electric wire (1) having a conductor (10) and an insulating coating (20) that coats the outer periphery of the conductor (10), the coated electric wire (1) having a flat portion in which the conductor (10) is in a flat shape that is long in the width direction in a cross section intersecting the axial direction, and in the cross section of the flat portion, the thickness of the insulating coating (20) is smaller than the thickness of the conductor (10). The insulating coating (10) has a width direction portion (21) along the width direction and a height direction portion (22) along a height direction intersecting the width direction as a flat portion on the outer peripheral surface, and a circula