A communication system comprises a first communication terminal (101) provided with an ID tag (106) and having a communication function for a first medium, a second communication terminal (102) provided with an ID reader (107) and having a communication function for a second medium different from the first medium, and a communication server (109) connected to the first and the second communication terminals. The ID tag stores terminal address information representative of an address of the first communication terminal. When the ID reader reads, as readout address information, the terminal address information from the ID tag, the second communication terminal informs the readout address information to the communication server. Supplied from the second communication terminal with the address of the first communication terminal as the readout address information, the communication server registers the first and the second communication terminals as a single communication terminal having the communication functions for the first and the second media.