To maintain temperature allowable range of components when heating value is increased, by making a board module of an assembly form where an outer I/O connector is attached on the side surface of a frame on which a circuit board is mounted, and an inner I/O connector is attached on the upper surface of the frame, and vertically mounting a power source module on a base plate of a pedestal, in a closely contact fixing state by using penetrating bolts.

A board module 1 is formed by arranging an outer I/O connector 12 on the side surface of a frame 5 and arranging an inner I/O connector 6 on the upper surface. Penetrating bolts are inserted in the respective linkage holes 33, in a state that a power source module and a front and a rear covers are brought into close contact with each other. After both ends are fixed with nuts, the respective modules are vertically mounted on a base plate 25 and fixed with a large number of screws 21b. After engaging connectors 10 of an inner cable 30 are connected with connectors 6 of the respective modules, a shield cover 32 is attached. Generated heat from electronic components 2 is effectively conducted from the frame 5 to the base plate 25 and a sattelite structure 22.