A storage controller manages address conversion information denoting the correspondence relationship between a logical address and a physical address of storage area (for example, a physical block) inside a flash memory. The storage controller uses the above-mentioned address conversion information to specify a physical address corresponding to a logical address specified by an I/O request from a higher-level device, and sends an I/O command including I/O-destination information based on the specified physical address to a memory controller inside a flash memory module. The memory controller carries out the I/O with respect to a storage area inside a flash memory specified from the I/O-destination information of the I/O command from the storage controller.