Provided is a high-capacity SSD that has the same form factor as 3.5-inch hard disk drives and has a structure where memory cards, such as standard M.2 SSDs, M.3 SSDs or nonstandard full-scale SSDs, are inserted in a horizontal sliding manner into an exterior having the same size as a 3.5-inch hard disk drive, and are provided in a multi-stage arrangement in the vertical direction. The SSD multiplier provides a high-capacity SSD case structure having a novel structure where a vertical backplane board is placed at a fixed position such that the case does not need to be disassembled even when an SSD memory card is replaced with another SSD memory card having a different length. Further provided is a case structure which can handle the various sizes of SSD memory cards that are used, where individual SSD memory cards have vibration resistance characteristics against external vibrations in XYZ-axis directions.