A mediation server 200 mediates a print demand from a client device 100 to a printing device 300. In order to elude a firewall F/W set between the mediation server 200 and the printing device 300, the printing device 300 first sends an HTTP request to the mediation server 200. The mediation server 200 sends back an HTTP response including a print demand to the printing device 300. Encrypted communication may be established between the client device 100 and the printing device 300 according to the following procedure. The mediation server 200 decrypts cipher data, which is encrypted with a public key by the client device, with a private key, re-encrypts the decrypted data with another private key, and mediates the encrypted data to the printing device 300. The printing device 300 decrypts the encrypted data with the public key and carries out printing. This arrangement enables the printing device to carry out printing in response to a demand from the client device via respective secure network environments.