A facsimile server carries out facsimile communication, and notifies a forwarding destination computer of the confidential data reception when the facsimile server has confidentially received communication data. The facsimile apparatus transmits the confidentially received data in accordance with a demand by the destination computer. The facsimile server encrypts and decrypts the received data by using an encryption key produced based on peculiar information of the facsimile server and the forwarding destination computer at the time of carrying out communication with the destination computer via a computer network.