A storage system using flash memories includes a storage controller and plural flash memory modules as storage media. Each flash memory module includes at least one flash memory chip and a memory controller for leveling erase counts of blocks belonging to the flash memory chip. The storage controller combines the plural flash memory modules into a first logical group, translates a first address used for accessing the flash memory modules belonging to the first logical group to a second address used for handling the first address in the storage controller, and combines the plural first logical groups into a second logical group.