To easily distribute a cryptographic key without complicating a device configuration or state management of an entire system in the case of cipher communication between terminals through a network.

A path opening request is transmitted from a transmitting side communication terminal 10 to a transmitting side address managing server 12 (S1), the transmitting side address managing server adds a public key to the path opening request and transmits it to a destination side address managing server 14 (S2), a key to be used for enciphering is generated by the destination side address managing server (S3), and that key is added to a confirming request and transmitted to a destination side communication terminal 16 (S4). In the destination side communication terminal, a confirmation response is transmitted to the destination side address managing server (S5), the key to be used for enciphering is enciphered with the public key by the destination side address managing server (S6), and the enciphered key is added to a path opening response and transmitted to the transmitting side address managing server (S7). The transmitting side address managing server deciphers the enciphered key (S8), adds the deciphered key to the path opening response and transmits it to the transmitting side communication terminal (S9).