PURPOSE: To efficiently perform fault analysis.

CONSTITUTION: If detecting a fault, a fault detecting means 9 of a device 2 reports this detection to a fault data preserving means 12, a data gathering indication means 10, and a faulty device number report means 11. As the result, the data preserving means 12 preserves faulty data of the device 2, and the indication means 10 outputs a signal of logical value '1' to a signal line 6, and the number report means 11 outputs a signal indicating number '2' of the device 2 to a signal line 7. When receiving these signals, internal state preserving means 8 of devices 1 and 3 preserve state data of the device 2.