PURPOSE: To hold the trouble information of high importance in a storage device by processing the trouble information stored in an external storage device after the revel of the trouble is decided in response to the importance of the collected trouble information.

CONSTITUTION: Processors 11W1n are connected to a system diagnosing device 3 via diagnosis interfaces 21W2n. The trouble information produced by processors 11W1n are collected by a trouble information collecting means 3A of the device 3 and delivered to a trouble level deciding means 3B. The means 3B analyzes the contents of the trouble information and decides the trouble levels according to the improtance. Then the means 3B starts a capacity checking means 3C for external storage. The means 3C checks whether an external storage part 3F includes an unstored area or not. If any unstored area is detected, the trouble information and the trouble level are stored in an unstored area of the part 3F via a trouble information storing means 3F. When the capacity of the 3F is saturated, the stored information of the minimum level is compared with the trouble level of the new information. Then the information of higher level is stored in the part 3F. While the information of the lower level is erased 3D or disused.