PURPOSE: To prevent the occurrence of a call fault by automatically performing a call connection with the terminals of other subscriber stations at the time of the faults of the subscriber stations or repeating lines.

CONSTITUTION: The data from a subscriber terminal 10 is summed up in a host computer 20. In this case, when an exchange/subscriber station 31 accommodating the host computer 20 is in an impossible state to be operated or a repeating line W52 is impossible to be communicated with, an exchange/ repeater station 41 judges that the call connection with the exchange/ subscriber station 31 is impossible in a state recognition device 60. An incoming terminal is judged as the host computer 20 by analyzing the incoming terminal address by an incoming terminal discrimination device 61, a host computer 21 for the backup of the host computer 20 is deduced at an incoming terminal switching device 62, and a call transfer is performed by switching the incoming terminal address. The call connection with the subscriber terminal 10 and a host computer 21 is performed through an exchange/repeater station 43 and an exchange/ subscriber station 32.