To easily detect a fault in a network without increasing the facilities or the like, by comparing the new path control information acquires by a data acquiring means with the path control information stored in a storage means and detecting the information on a part where the path control information is changed.

In a normal state, the path control information on a network element 11 is fetched via a data acquiring part 121 of a data processor 12 and stored in a storage part of a storage device 13. Then the path control information on the element 11 is acquired at every fixed time via the part 121. The path control information stored in the storage device 13 is compared with the acquired new path control information to check whether the latter information is changed. If the relevant information is changed, it is decided that a fault occurs on a network and a part where the path control information is changed is extracted. Thus, it is possible to specify the fault part by analyzing the extracted part.