A communication relay system relays communications between communication terminals performing the communications according to a plurality of communication protocols. The communication relay system includes pseudonymous identification information acquiring sections associated with respective communication protocols. Each of the pseudonymous identification information acquiring sections acquires pseudonymous identification information which is information according to the associated communication protocol and is different from terminal identification information for identifying each of the communication terminals. The communication relay system includes a communication relay section which, when receiving communication information according to a communication protocol from one of the communication terminals, replaces the source terminal identification information included in the communication information with pseudonymous identification information acquired by the pseudonymous identification information acquiring section, and transmits the communication information after the replacement to another one of the communication terminals.