PURPOSE: To reduce the scale of a test signal generation detecting circuit and to simplify its constitution by using a modulating and demodulating circuit for a test signal generating circuit for the continuity test of a trunk, and further using a transmitting and receiving circuit for a detecting means.

CONSTITUTION: When a test request signal arrives at a control circuit 11 from a trunk 1 to be tested, a control circuit 10 connects the trunk 1 to be tested to a testing device 2, and the modulating and demodulating circuit 7 sends out a test signal, which is detected by an MFC transmitting and receiving circuit 8. When a continuity test of the objective trunk 1 is completed, the control circuit 10 disconnects the testing device 2 from the tested trunk 1 and returns to the original state.