METAL CORE SUBSTRATE FOR IN-VEHICLE ELECTRICAL JUNCTION BOX

Provided is a metal core board which has a preferable function for a vehicle-mountable junction box, specifically, is reduced in size or improved in mounting efficiency. A metal core board 11 for a vehicle-mountable junction box, which is mountable on the vehicle-mountable junction box, wherein a core plate 31 forming an intermediate layer of the metal core board 11 has a plurality of slits 32 and an island 34 surrounded by separating connection parts 33 present between the slits 32; and in the state where the island 34 is held between insulating layers 41a stacked on both of two surfaces of the core plate 31, through-bores 46 are formed at the separating connection parts 33 to remove the separating connection parts 33 and the island 34 is made electrically independent from a remaining part of the core plate 31 while being held between the insulating layers 41a. Thus, a plurality of circuits can be formed.