When a failure occurs in a network or in a network apparatus, a connection state of the network is changed. There is provided a network configuration estimating apparatus for knowing logical route information quickly after a failure occurrence in accordance with information collected from network apparatuses, although it is conventionally difficult to know this information quickly. The network configuration estimating apparatus executes: a process of generating network configuration information such as physical and logical topologies from information collected in advance; a process of monitoring a network failure; a process of calculating a network configuration to be estimated after a network failure occurrence, from the network configuration information generated in advance and network failure information; a process of visually displaying the calculated network configuration; and a process of managing history of calculated network configurations.