In IP telephony systems, it has become impossible to detect the location of installation of a telephone terminal from the telephone number, since an IP telephone terminal can be installed in an arbitrary location. Also, even if one observes the calling party number presentation at the time of an incoming call, it has become impossible to grasp from where the calling party is placing the outgoing call. It is possible that, within an IP telephony system, a terminal location detection means is configured and the installation location of a telephone terminal is detected simultaneously with the registration of the telephone terminal. In addition, the problem can be solved by configuring, in an IP telephony server, a device of reporting location information about the correspondent to the telephone terminal and by configuring, in the telephone terminal, a device of displaying the received positional information.