The card mounting configuration includes a card with a height that is approximately half that of conventional cards and integration of a front plate and a back plate of the card with a support to prevent circuit board distortion. A card ejector is attached on the front plate, and a plug-in connector is provided on the back plate. A housing contains two levels, upper and lower, wherein six cards are mounted into each level. A plug-in connector passes through a hole in a back board of the housing and is connected to a part of an external line connector that is exposed on the inside of the housing.