A portable terminal device with built-in GPS (global positioning system) has: a telephone radio part for wirelessly transmitting and receiving latitude information and longitude information; a GPS radio part for receiving data from a GPS satellite; a storage unit for storing the data received in the telephone radio part; a map information part for storing map information; and a control unit for setting the designated movement range of another portable terminal device with built-in GPS on the map stored in the map information part then sending it to the another portable terminal device, and receiving data on the current position of the another portable terminal device to be computed by itself.