PURPOSE: To attain sure line connection by eliminating the need for storing data in advance to discriminate a call signal and discriminating accurately a call signal from a telephone exchange even when the terminal equipment is installed to any district.

CONSTITUTION: Upon the receipt of a signal sent on a telephone line 5 in the communication standby state of the equipment via a call signal detection circuit 15, a CPU 7 activates a timer 21 to measure a period of the signal, that is, an ON time and an OFF time and to measure a frequency of the signal and to store data to a storage area 9a of a RAM 9. The CPU 7 measures the ON time, the OFF time and the frequency of the signal received continuously to the said signal and stores the data to the storage area 9a of the RAM 9. The CPU compares both the signal data and discriminates the signal to be a call signal when the data are almost the same and connects the telephone line 5 and then starts the communication.