A support device for supporting at least one electric harness where it passes through a through hole in a composite material structure, the structure presenting two faces into which the hole opens out, the device including a first element made of dielectric material presenting a first bearing surface designed to be applied against one of the faces of the structure and a sleeve having a first end secured to the first bearing surface and having outside dimensions that are smaller than those of the hole so as to be capable of being inserted therein, and a second element made of dielectric material presenting at least one second bearing surface suitable for being applied against the other face of the structure.