A portable telephone is provided with a first memory 1, a second memory 2, a first CPU 3, a second CPU 4, an interface 5, an antenna 6, a battery 7, and a switch 8. When buildings are collapsed and the user of the portable telephone is left under rubble, a rescuer transmits an emergency signal toward the collapsed site by using a transmission unit. The emergency signal includes key information. The signal is received by the portable telephone and then sent to the first CPU 3 via the antenna 6 and the interface 5. The first CPU 3 compares the key information included in the received signal with key information stored in the first CPU 3. A rescue signal is transmitted via the antenna 6 and the interface 5 on condition that both pieces of key information match. The rescue signal is received by the rescue party and as such, the position of the portable telephone is determined.