Abstract: A modular structure of a storage device applied in a network attached storage (NAS) system includes: a control device, having a system board, and the system board having a positioning board and a positioning space; a storage device, installed on the positioning space of the system board, and having a shock-resisting element sheathed onto the storage device; a casing, covered onto the storage device, and having a connecting device disposed on the casing; and a ventilating device, covered on an external side of the casing, and having a ventilation body and a ventilation passage interconnected with each other, and a ventilation opening disposed at an end of the ventilation passage. The storage device can be expanded by a modular design, and the invention can achieve better shock resisting and heat dissipating effects of the storage device, so as to enhance the stability, safety and competitiveness of the storage device.