A first index value, which is an index value of a deflection amount of a structure generated at an observation point, and a second index value, which is an index value of a deflection amount at a designated position in the structure, are acquired based on the number of moving objects formed in a formation moving object, an entry time point, an exit time point, and environment information. An estimated value of the deflection amount of the structure at the designated position is derived based on time-series data measured at the observation point, the first index value, and the second index value.