PURPOSE: To prevent wires from being broken due to stress concentration by coating all of the wires with an outermost coating considering the difference in th finished diameters of the wires so that the finally finished outer dimension is uniform.

CONSTITUTION: A conductor 1 with a required insulation coating 2 of a wall thickness (a) has a finished outer diameter A. Similarly, a conductor 3 with a required insulation coating 4 of a wall thickness (b) has a finished outer diameter B. A multiple number of these wires A and B of different outer diameters are arranged side by side in a plane and coated with an outermost insulation coating 5 so that their outer dimension is C by coating the conductor 1 with an outermost insulation coating of the thickness a' and coating the conductor 3 with an outermost coating of the thickness b'. As a result the finished outer dimension C is constant. When the wires are bent, the curvature radii are identical for all of the insulated wires so that breakage due to stress concentration is prevented.