A mounting adapter capable of reducing manufacturing cost includes: an HDD tray to which a hard disk drive is fixed; an HDD holder fixed to a housing and receiving the HDD tray inserted from a Y-axis direction; and a connector board so mounted to the holder as to be movable in a plane perpendicular to the Y-axis direction, and provided with a connector with which an HDD connector is connected. The suitable mounting adapter enables the HDD connector and the connector of the connector board to be engaged optimally even though the central axes of the HDD connector and the connector of the connector board are not aligned.