A volatile management memory stores management information for managing a use state of a storage medium. A management information storing unit divides the management information into plural division pieces and individually stores them in the storage medium. A main controller receives a command from a host device while the division pieces are being stored, performs data processing for the storage medium in response to the command between each division piece is stored, updates the management information divided into the division pieces according to the data processing content, and creates a log representing an update content of the management information. A log storing unit stores the log in the storage medium. A restoring unit reads the division pieces stored in the storage medium to the management memory as the management information, updates the management information according to the log stored in the storage medium, and restores the updated management information.