1. An information processing apparatus comprising: modification means for acquiring M information sets each including N pieces of individual information and modifying at least partially the N pieces of individual information of each of the M information sets such that correlations among the N pieces of individual information are emphasized, where N is an integer equal to or greater than 2 and M is an integer equal to or greater than 1; generation means for generating a reference information set including N pieces of individual information for use as a reference in a calculation of similarity, from the M information sets each including N pieces of individual information modified by the modification means; and similarity calculation means for acquiring, as a comparative information set, a new information set including N individual information elements and calculating the similarity of the comparative information set with respect to the reference information set produced by the generation means.