A method of estimating a trouble in a network is disclosed, including the following steps: displaying a model network in which the network is modeled by each combination of a network apparatus and a connection; inputting information of trouble portion in the model network and trouble symptom; registering at least trouble portion, trouble symptom, cause portion, and frequency of past trouble instances occurred in the model network to an instance database; retrieving the instance database using the input trouble portion and trouble symptom as retrieval keys; and estimating and displaying cause of the trouble based on the cause portion and frequency of a retrieved instances record. The past trouble instances accumulated in the instance database can be retrieved by the instance retrieval unit using the trouble portion and trouble symptom as the retrieval key. The network trouble estimation apparatus can estimate the cause portion at high accuracy.