PURPOSE: To provide a countermeasure to an increment of the feed capacity without increasing the number of power supply layers, by supplying the power to the power supply layers at the periphery and the center of a back board.

CONSTITUTION: A feed member 15 is fixed at the periphery of a back board 10 and at the same time connected electrically to the power supply layers of the board 10. While a feed member 13 is fixed to a logical card attachment surface (at the side of a connector 11) of the board 10 and connected electrically to the power supply layers of the board 10. Thus an external power supply is connected to the member 15, and therefore the power is supplied to the power supply layer at the periphery of the board 10 via the member 15. At the same time, the power is supplied to the power supply layer at the center of the board 10 via the member 13. As a result, it is not required to increase the number of power supply layers even through the feed capacity is increased.