PURPOSE: To efficiently execute analysis by classifying fault information according to the definition of classification and storing the content of the fault information while being separated into summary information and detailed information, thereby facilitating the grasp of important fault information and a rough fault status.

CONSTITUTION: A fault information classification control section 113 receiving fault information at first from a fault information generating section 112 selects and references an effective table among plural fault information classification tables, references an importance classification corresponding to a message NO of the received fault information to discriminate the importance classification. When the discrimination indicates a major alarm, a detailed information log record is generated and the detailed log is stored in a detailed information log file 23. Then a major alarm summary log record is generated and its major alarm summary log is stored in a log file 21. When the discrimination indicates a minor alarm, the detailed log record is generated and its detailed log is stored in the file 23. Then a minor alarm summary log record is generated and its summary log is stored in a file 22.