Estimation is carried out with high accuracy based on flow quality information in a situation where, although a set of links that may have a flow passing through is known, which of such links the flow passed through cannot be identified, such as multi-paths routing, load distribution routing, and the like. A device for estimating a quality-degraded location includes a flow quality information collecting section that collects communication quality of a flow of a network, a routing information collecting section that collects routing information of the network, a determining section for determining a quality-degraded flow and a quality-non-degraded flow based on the flow quality information to determine a link through which the flow passes from the routing information of the network, a non-degraded link elimination section that eliminates a link not configuring multi-paths as a non-degraded link without eliminating a link configuring multi-paths as a non-degraded link, for a link on a path of the flow, with respect to the quality-non-degraded flow, and a degraded link determining section for determining a degraded link from links not eliminated as the non-degraded links.