According to the embodiments, there are provided semiconductor memories that are mounted individually on two sides of a mounting board; a controller that is mounted either on an obverse side or a reverse side of the mounting board, and performs read and write control of the semiconductor memories; and a connector that is deviated in a lateral direction from the controller so as not to overlap the controller, is mounted either on the obverse side or the reverse side of the mounting board, and transfers a signal exchanged between the controller and outside.