Abstract: [Problem] To provide an anonymous communication system which ensures anonymity, with which a user can be identified if necessary, and which has a high degree of social credibility. [Solution] A user computer 11 transmits to a management computer 21 electronically signed subscription application data signed using a first signature key capable of being used with another communication system. The management computer 21 verifies the electronic signature of the subscription application data using a first public key, and if the validity of the electronic signature can be verified, generates and encrypts a second signature key and transmits the encrypted second signature key to the user computer 11. The user computer 11 generates electronically signed receipt data that have been signed in duplicate using the first and second signature keys, and transmits the receipt data to the management computer 21.