To accurately estimate a damaged spot of an OPGW (optical fiber composite overhead ground wire) by specifying, as the damaged spot, a spot where the altitude of a construction spot or its inclination looked from a start point is larger.

First of all, an information processor locates the lowest sag point in a hydrogen generation section of the OPGW (S501), and sets the lowest sag point as a search start point (S502). Next, the altitudes of steel towers in a search direction are set in an arrangement P(n)(1nN, N is the total number of the steel towers to be searched) (S506), and a steel tower (n) is searched with n used as a variable. When the steel tower (n) has a caching section (Y in S510), if the altitude P(n) of the steel tower (n) is higher than the altitude P(n-1) of a steel tower (n-1) (Y in S509), the caching section is stored as a candidate for the damaged spot (S511). Search is performed in both directions from the lowest sag point, and when the search finishes (N in S513), a candidate having a bigger difference in altitude from the lowest sag point or inclination is decided as the estimated damaged spot, from among stored candidates (S518).