A bundle of electric wires has a first length and a first diameter. A tubular braided wire has a second length which is shorter than the first length and a second diameter which is larger than the first diameter. The bundle of electric wires is passed through the braided wire, and then a connector is connected to each of both ends of the electric wires collectively. The connector having a third diameter which is larger than the first diameter. The braided wire is stretched such that both ends thereof are fixed on the respective connectors to form a reduced-diameter portion therebetween which is fitted on an outer periphery of the bundle of the electric wire. A conductive retainer is attached on the reduced-diameter portion to maintain a length and a diameter of the reduced-diameter portion.