An internet protocol phone system having a plurality of internet protocol networks which are provided with internet protocol address systems in which local internet protocol addresses and global internet protocol addresses differ, and are mutually connected, and an internet protocol address translation device which is connected to the local internet protocol network, gives the local internet protocol address and the global internet protocol address to an internet protocol phone device, and obtains the local internet protocol address and the global internet protocol address from the internet protocol phone device, in which when it is detected that the internet protocol phone device which is connected to the local internet protocol network enters a calling state, the internet protocol address translation device gives the global internet protocol address to the internet protocol phone device thereof, and when it is detected that the call of the internet protocol phone device is finished, the internet protocol address translation device obtains the global internet protocol address from the internet protocol phone device.