An IP telephone system comprises a main device that manages outgoing and incoming calls of an IP telephone device, an external storage device storing network configuration information and telephone device configuration information, and an IP telephone device comprising a first interface section that uses in connection to the external storage device and a second interface section that uses in connection to a network. When automatically carrying out internal setting by connecting the external storage device to the first interface section, the IP telephone device obtains the network configuration information and the telephone device configuration information from the external storage device and, based on the obtained network configuration information and telephone device configuration information, carries out network setting and telephone device setting. The IP telephone device accesses the main device through the second interface section based on the setting and performs confirmation of the set contents.