A storage device, enabling elimination of redundant write operations of non-selected data and enabling optimization of arrangement of pages to a state efficient for rewriting, having two flash memories which can be accessed in parallel, a page register for acquiring data in parallel from the flash memories and temporarily storing the same, and a control circuit having a built-in RAM in which is constructed an address conversion table for managing correspondence between logical addresses and physical addresses in units of data stored in parallel in the page register, wherein data is rewritten by updating of the address conversion table and additional writing into a storage medium.