To recognize the abnormality of a communication line between a guard center device and a base station without needing any inspection of a personnel by managing the communication state of a communication network while including a guard terminal equipment and recognizing the communication network abnormal in communication line among the communication networks.

When a CATV network 52 between a base station 31 and guard terminal equipment 41 is physically cut and a communication line becomes abnormal, a CATV guard center device 2 executes polling for plural times on guard terminal equipment 41-1 via the base station 31, but a response is not given. The CATV guard center device 2 recognizes it as the abnormality of guard terminal equipment 41-1 containing the CATV network 52 and reports it to a host guard center device 1 as the abnormality of guard terminal equipment 41-1. Namely, unnecessary management such as the investigation of guard terminal equipment 4 is not required and the efficiency of a guard job can be improved by recognizing the communication line abnormality of the CATV network 52 between the CATV guard center device 2 and the base station 31.