An electrical junction box for distributing electric power in a vehicle includes a metal core substrate provided with a core metal assembly having two core metal plates arranged with a gap, an insulating layer embedded in the gap and covering surfaces of the core metal plates to integrate the core metal plates, and electronic components. Electric power from a battery is inputted into the core metal plate, and electric power from an alternator is inputted into the core metal plate. The electronic components are provided with a plurality of attaching portions soldered or screwed to the metal core substrate. At least one of the attaching portions is attached to the core metal plate, and at least one of the attaching portions is attached to the core metal plate.