1. A filtering device, comprising: an evaluation value deriving module that derives, for a pair of comparison targets having mutual relevance, multiple evaluation values indicative of correlations with any one of extracted parts extracted from one of the comparison targets and multiple extracted parts that are extracted from the other comparison target, respectively; an evaluation range setting module that sets an evaluation range of the evaluation values, the evaluation range having one of boundaries at the evaluation value with the highest correlation among the multiple evaluation values; and a difference value determining module that determines whether the evaluation value with the highest correlation is valid as a difference value based on the multiple evaluation values and the evaluation range.