PURPOSE: To shorten the time for looking into the cause at the time of abnormality by covering and detecting all the abnormalities generated in the dual-route carrier circuit in a remote monitoring control.

CONSTITUTION: A carrier signal is taken out from each communication line of a route 1 and a route 2, the detections are performed in a DEM 1L-1 and 2L-1, data is taker out for every word in S/P circuits 1L-2 and 2L-2, and the data is stored in memories 1L-3 and 2L-3. By matching the word address of the stored data and the address of a control circuit 3, the data of the memories 1L-3 and 2L-3 is moved to memories 1L-4 and 2L-4 and is stored. Subsequently, each of this stored data is taken out by every 1-bit, the data is compared in a mismatching detection circuit 4. In the case of the mismatching, the trigger signal S1 of the generation of an abnormality is outputted to a memory bi-coder 6. By this trigger signal S1, the carrier signals S1 and S2 and detection signals S3 and S4 of each route are recorded and a fault generation status is judged.