1. A valid medium management system, comprising: an original data storage system storing an original data; a storage unit storing a key corresponding to an ID number specifying the original data storage system; and a valid medium issuing system obtaining a key corresponding to the ID number from said storage unit, and putting a signature of a valid medium in a non-falsified area of a storage medium using the key, wherein said original data storage system decrypts the signature of the valid medium from the non-falsified area, and records the original data on the storage medium.