Electrical junction box

A first insulating board (133) is located at a rear side of an on-vehicle device provided with an electronic component. The first insulating board has a first face opposing to the on-vehicle device and a second face which is opposite to the first face. A first circuit (131) is provided on the first face of the first insulating board (133) and includes a signal transmission circuit. A second circuit (132) is provided on the second face of the first insulating board (133) and includes a power transmission circuit. An electrical junction box shall be provided which can positively reduce adverse effects of spike noises and others without complicating its construction.