A method of preventing a high-frequency noise generated in an electronic device, remaining in a grounding cable as a standing wave and transmitted to electric devices, is disclosed, which method including disposing, directly or via an insulating layer, a non-metallic conductive material having a slight electric resistance, on a conductor of the above-mentioned grounding cable, making the electric resistance of the non-metallic conductive material consume the high-frequency noise flowing on the conductor surface of the grounding cable by virtue of a skin effect, whereby resonance of the high-frequency noise is reduced. Resonance of the high-frequency noise generated from various electronic devices in an office building and the like can be easily reduced. Consequently, various disadvantages due to high-frequency noise can be avoided. In addition, the slight electric resistance R of the non-metallic conductive material and inductance L of the metal conductor are set to satisfy the formula: 2&pgr;fL/R≦1, so that the resonance of a high-frequency noise can be reduced.