To apply twisting action to a wire around its own axis prior to preforming and make this action quality almost equal to a double twisting type generated to the wire during a laminating process.

A cord formed of at least a first pair of wires 2a and a second pair of wires 2b of different diameters disposed at random in a cross section part is formed by disposing a twister 16 in a nacelle 7 of a double twisting laminating machine The twister 16 rotated at the double speed of the rotating speed of an impeller 5 in the opposite direction to the rotating direction of the impeller 5 neutralizes internal torsional stress generated to the wires 2a, 2b as the action of double twisting performed by the action of the impeller itself. A preforming process applied to the wires 2a, 2b arranged parallelly in the axis of the same plane can thereby be controlled much better.