A high-speed transmission connecting sheet 10 includes a first elastomer connector 1E formed on a top sheet 1, a second elastomer connector 2E formed on a bottom sheet 2, third elastomer connectors 3E formed on high-speed transmission boards 31 through 33, and fourth elastomer connectors 4E formed on intermediate layer boards 41 and 42. These elastomer connectors provide three-dimensional connection between the multiple high-speed transmission paths 3C formed on the high-speed transmission boards 31 through 33. A plug housing 5 has the high-speed transmission connecting sheet 10 installed therewithin, with the first elastomer connector 1E disposed at one inner wall of opposing inner walls, and the second elastomer connector 2E disposed at the other inner wall of the opposing inner walls. Receptacle pins 1P are disposed on the first elastomer connector 1E, and plug pins 2P are disposed under the second elastomer connector 2E. Both ends of the high-speed transmission connecting sheet 10 are pressed into contact, whereby the receptacle pins 1P and the plug pins 2P are connected through the multiple high-speed transmission paths 3C.