To appropriately allocate address port information indicative of a communication source and a communication destination to a connection request in IP telephone communication between terminals connected to the internet.

The present invention relates to a system for performing IP telephone communication using an IP telephone application, comprising a group including one or more calling-side information terminals and a gateway device 40 connected to the internet 50, and a called-side terminal 52 connected to the internet 50. The calling-side information terminal introduces an IP telephone application from the gateway device 40 and transmits an IP telephone connection request toward the called-side information terminal 52. The gateway device 40 then comprises a function for allocating address port information required for setting up an IP telephone call between the calling-side and called-side terminals to the IP telephone application and a function for receiving the IP telephone connection request transmitted by the calling-side information terminal, appropriately translating the address port information of a transmission source and a transmission destination and transferring the information.