A translator is connected to a first network for transferring data in a first protocol, to a second network for transferring data in a second protocol, and to a translation server to which other translators are connected, for retaining translation information for a protocol translation between the first protocol and the second protocol. The translator generates a second address in the first protocol corresponding to a first address in the second protocol provided to a terminal accommodated in the second network. It retains a correspondence between the first address and the second address as the translation information and registers the correspondence at the translation server.