PURPOSE: To reduce crosstalk noise caused between wirings and to alleviate the deviation of logic timings in a high speed signal transmission by connecting a daughter board to a back plane through an exchange board on the rear surface of a housing.

CONSTITUTION: When a transmitting signal on a daughter board 2 is measured, the male connector 8 of the daughter board 2 is removed from the inner female connector 7 of a back plane 6, and connected to the female connector 13 of an exchange board 11. The male connector 12 of the exchange board 11 is inserted into the female connector 9 outside the backplane to be connected. ln this case, the disposing order of signal pins 10 of the male connector 9 of the daughter board 1 in a housing 1 is in a X-Y direction, but it becomes Y-X direction on the rear side of the housing 1 so that the positional relationship of the signals is different. Accordingly, the daughter board 2 cannot be simply connected to the rear surface of the housing 1. Thus, the exchange board 11 is required to match the positional relationship of the signals, and the positional relationship of the signals can be matched by a wiring pattern in the exchange board 11.