The second main cover CVB may have an area smaller than that of the first main cover CVU. The second main cover CVB covers the entire module board BDH of the memory module 110 from below, but may be configured to expose the memory connector MCN. The first short side SS1 of the second main cover CVB is placed inside the first short side SS1 of the first main cover CVU, and may be located inside the end portion of the memory connector MCN. The first short side SS1 of the first main cover CVU may be arranged on the first short side SS1 of the module board BDH, but is not limited thereto.