PURPOSE: To speedily and suitably execute maintenance related to the fault of the exchange system even by a maintenance person not having special knowledge so much.

CONSTITUTION: When autonomous fault information is outputted from a suspected exchange system 2 after a fault is caused generated at the system 2, an inference part 13 receives the information through a system interface part 14, infers a point to be diagnosed by using various knowledge in a data base part 20 and outputs an instruction to a diagnosis part 12 based on the inferred result. According to the instruction, the diagnosis part 12 diagnoses the relevant point of the suspected exchange system 2. Based on this diagnosed result and the information in the data base part 20, the inference part 13 leads out the fault points in the order of high suspection probability and outputs the result through a user interface part 11 to a console part 1. The maintenance person takes required countermeasure by observing the result outputted to the console part 1.