An identification information management system according to the present invention comprises a plurality of terminals communicable with servers and a site management apparatus which manages site containing the terminals. The terminal has an identification information processing unit which assuming that a one-way hash function is f(x) and a terminal-unique ID is a, generates values x satisfying a conditional equation f(x)=a as identification information. When acquiring multiple items of identification information, the site management apparatus substitutes the identification information as the value x into f(x) and decides whether f(x)=a is satisfied, thereby deciding the terminals.