A secondary memory device includes: a substrate and a housing configured to accommodate at least a part of the substrate. The substrate has upper and lower opposed surfaces and includes a first region in which a first semiconductor device is mounted on the upper surface and a second region in which a second semiconductor device is mounted on the upper surface. The housing includes a first sub-housing covering the upper surface of the substrate at the first region and the first semiconductor device. The first sub-housing does not extend to cover the upper surface of the substrate at the second region.