An electric wire conductor having both flexibility and a space-saving property, a covered electric wire, and a wiring harness containing such an electric wire conductor. The electric wire conductor contains a plurality of elemental wires, and has a flat portion in which a cross-section intersecting an axial direction of the wire strand has a flat shape. In the cross-section of the flat portion, a vacancy ratio defined as a ratio of vacancies not occupied by the elemental wires is 17% or higher. Further, a covered electric wire contains the electric wire conductor and an insulator covering the electric wire conductor. Furthermore, a wiring harness contains the covered electric wire.