Disclosed is a packet-switched communication apparatus (DNS proxy server) receiving and forwarding messages which are used to obtain an address corresponding to a domain name assigned to a device connected to a network from the domain name and to obtain such a domain name from the address. The communication apparatus comprises mapping retaining means for retaining mappings between network-dependent parts of addresses which are used in a first network and address translators; address translator selecting means for selecting an address translators, based on an address included in a received packet; address obtaining means for obtaining a substitutive address to replace the address included in the received packet from the selected address translator; and address replacement means for replacing the address included in the received packet by using the obtained substitutive address.