[Problem] To achieve a voice communication system which communicates between two networks that use partially overlapping address spaces.
[Solution] According to the present invention, first and second networks are connected to one another by means of a gateway device provided with: a first protocol stack which manages transmission and reception addresses of communication packets in the first network; a second protocol stack which manages transmission and reception addresses of communication packets in the second network; and a call control unit which, upon reception of a communication packet from either network, determines the transfer destination network and transfer destination address of the packet on the basis of call destination information included in the packet.