The storage system of the present invention preserves data long-term by using memory devices such as flash memory devices. A flash memory mounting unit of a storage apparatus has a plurality of flash memory devices. Logical devices are set up in the storage region of the flash memory devices. A start-up scheduler controls start-up of internal refresh processing and external refresh processing. A refresh function management table respectively manages the method of refreshing the data stored in the flash memory devices and the refresh time, for each logical device. The start-up scheduler, on discovering that a logical device has reached its refresh period, sends a start-up command to the storage apparatus or external apparatus, to start-up internal refresh processing or external refresh processing.