To provide a communication system by which peer-to-peer communication is performed on confirming that a device of a connection partner is a correct device even when at least one device does not have a global IP address between the devices at mutually different networks.

A server 101 transmits a connection request A from a request issuance device 102 to a request acceptance device 103 as a connection request B. Connection information to the request issuance device 102 and a disposable password are included in the connection request B. The request acceptance device 103 transmits the disposable password received from the server 101 to the request issuance device 102 as a response password using the connection information received from the server 101. The request issuance device 102 maintains connection on confirming that the connection partner is the request acceptance device 103 by the received response password and the transmitted disposable password.