An electric junction box includes a circuit construct as an internal circuit component. The circuit construct includes relays mounted on one side of a printed circuit board and bus bars fixed on the other side of the printed circuit board. The circuit construct is divided into a basic standard circuit construct and an optional circuit construct, in which the basic circuit construct is used in a plurality of grades of a vehicle family, in different vehicle families of the same grade, or in all vehicle families. Multiple circuit constructs may be combined as necessary and put in a side by side relationship. On the bus bar side of the circuit constructs, a heat sink is attached such that it is exposed to the opening provided on the case of the electric junction box.