A communication system comprising: a transmission and receiving unit of a management system configured to receive a request for establishing a session between a first terminal and a second terminal, the request being sent from the first terminal, and the request including requesting so that the session being restricted for a third terminal, other than the first terminal and the second terminal, to participate in; a session management unit configured to establish the session between the first terminal and the second terminal (lOdb) in accordance with the request received by the transmission and receiving unit; and a determination unit configured to prohibit the third terminal from participating in the session between the first terminal and the second terminal when the third terminal requests to participate in the session established by the session management unit, characterized in that the communication system further comprises: a memory configured to store therein each of the plurality of terminals in association with teleconferencing terminal candidates with which each terminal can establish a session; and a display control unit configured to display, on a display of the third terminal (1 Ocd), the teleconferencing terminal candidates associated with the third terminal as stored in the memory in such a manner as to allow a user of the third terminal to make a selection, wherein the display control unit is configured to display the teleconferencing terminal candidates in association with a communication state: an "on line" and communication possible state where a session can be started, an "on line" and busy state where a session is ongoing and an "off line" state where the teleconferencing terminal candidate is not connected with the communication system, and to display a teleconferencing terminal candidate as having an "off line" state when the teleconferencing terminal candidate participates in a session designating presence of participation restriction. a transmission and receiving unit of a management system configured to receive a request for establishing a session between a first terminal and a second terminal, the request being sent from the first terminal, and the request including requesting so that the session being restricted for a third terminal, other than the first terminal and the second terminal, to participate in; a session management unit configured to establish the session between the first terminal and the second terminal (lOdb) in accordance with the request received by the transmission and receiving unit; and a determination unit configured to prohibit the third terminal from participating in the session between the first terminal and the second terminal when the third terminal requests to participate in the session established by the session management unit, characterized in that the communication system further comprises: a memory configured to store therein each of the plurality of terminals in association with teleconferencing terminal candidates with which each terminal can establish a session; and a display control unit configured to display, on a display of the third terminal (1 Ocd), the teleconferencing terminal candidates associated with the third terminal as stored in the memory in such a manner as to allow a user of the third terminal to make a selection, wherein the display control unit is configured to display the teleconferencing terminal candidates in association with a communication state: an "on line" and communication possible state where a session can be started, an "on line" and busy state where a session is ongoing and an "off line" state where the teleconferencing terminal candidate is not connected with the communication system, and to display a teleconferencing terminal candidate as having an "off line" state when the teleconferencing terminal candidate participates in a session designating presence of participation restriction. a memory configured to store therein each of the plurality of terminals in association with teleconferencing terminal candidates with which each terminal can establish a session; and a display control unit configured to display, on a display of the third terminal (1 Ocd), the teleconferencing terminal candidates associated with the third terminal as stored in the memory in such a manner as to allow a user of the third terminal to make a selection, wherein