Regular chip packages that store user data therein and error-correction chip packages that store an error correction code therein are mounted on a module substrate. The module substrate has first and second mounting areas of different coordinates in an X direction, and the second mounting area has third and fourth mounting areas of different Y coordinates. The regular packages are oppositely arranged in the first mounting area on a surface and the back surface of the module substrate. The error-correction chip packages are oppositely arranged in the third mounting area on the surface and the back surface of the module substrate. A memory buffer that buffers user data and an error correction code is arranged in the fourth mounting area.