PURPOSE: To allow a subordinate station equipment to supervise a fault information as to transmission block differently from usual alarm information in the system where a host station equipment supervises alarm information from the subordinate station equipment.

CONSTITUTION: A subordinate station equipment 20 is provided with a 2M highway interface block 21 that detects an alarm of a message transmission block 22 itself, changes a bit of a time slot and sends the resulting slot to a host station equipment 10, and the host station equipment 10 is provided with a 2M interface block 12 that extracts a time slot of a subordinate station from a 2M ground line, with a shift register circuit 13 outputting a bit for alarm report of the message transmission block 22 from the time slot and with a message reception block 11 recognizing respectively output information from the shift register circuit and usual alarm information from a subordinate station.