There is provided an identifier authentication system in which information requesting users can share all predetermined information held in a plurality of information providing servers.In the identifier authentication system, when an identifier holding user 19 presents an identifier to an information requesting server 15, the information requesting server 15 asks a location management server 13 about a location of an information providing server 14 corresponding to the presented identifier, the location management server 13 returns the confirmed IP address of the information providing server 15 corresponding to the presented identifier to the information requesting server 15 based on the location information, the information requesting server 15 accesses the information providing server 14 corresponding to the confirmed IP address by using the confirmed IP address, and receives predetermined information corresponding to the presented identifier from the accessed information providing server 14.