Disclosed is a network monitoring method, a network monitoring apparatus, a line failure prevention system and a computer program of network monitoring apparatus, wherein the network monitoring method includes: a predicted amount of rainfall obtaining step of obtaining a predicted amount of rainfall generated in a predetermined time in a current line route; a prediction step of predicting whetheror not a line failure occurs in the current line route caused by the predicted amount of rainfall assuming it rains actually in the current line route with an amount of rainfall substantially equivalent to the predicted amount of rainfall in the predetermined time in the current line route; and a change instruction step of instructing the radio communication network to change the current line route into a different line route on which it is predicted that no line failure caused by rainfall occurs and to control the radio communication network to change the current line route into the different line routes, before the predetermined time passes.