PURPOSE: To prevent formation of a protrusion part on a floor material surface owing to the thickness of a cable when wiring is carried out by means of an under carpet system and to facilitate wiring and exchange of wiring.

CONSTITUTION: First, a cushioning material 1 wherein a resin sheet 2 is laminated on the one surface and a mold release sheet 3 is laminated on the other surface through an adhesion material layer 4 is prepared. Secondly, a groove 1a is cut and formed from the surface of the mold release sheet 3 of the cushioning material 1. Wiring is effected in the groove 1a. Thirdly. the mold release sheet 3 is peeled. A floor material B is then adhered on the adhesion material layer 4.