An information processing device (10) is equipped with an observation data acquisition unit (24) that acquires observation data (RD) of a deterioration index, which is an index related to deterioration of a vehicle, and a prior estimation data determination unit (30) that is capable of determining prior estimation data (PE) to be used in a data assimilation process in order to estimate the deterioration index by selecting, based on the observation data, from among a plurality of prior estimation data candidates (PEC) that are prepared in advance.
