PURPOSE: To immediately conduct a system/subscriber test from a maintenance center by connecting a call line required for the system/subscriber line test to a general telephone network and connecting a trunk for call test and a sound source for test on an exchange-side to a fault device.

CONSTITUTION: When the fault occurs in an output trunk 13, for example, it is detected in an operation device band subscriber circuits 4 and 5 are called. When a connection device 3 detects the incoming call, it transmits an incoming call message and incoming ringing to a telephone system for call test 2. A maintenance man inputs a response command to a maintenance operation terminal 1. Thus, the terminal 1, and the system 2 are connected to the maintenance operation device 26 and a channel switch 19. When the maintenance man supplies the test command for conducting the test of the output trunk 13 and connects the output trunk 13 to an input trunk for test 15, they are connected to a call test trunk 25. Thus, the maintenance man can recognize the presence or absence of tone from a tone source, a level and the like in the system for call test 2.