1. A search method of searching for pairs of pieces of information having a similarity not equal to or greater than a predetermined similarity, comprising: obtaining a rate of information elements constituting a piece of information that are present in common between pieces of information so that the pair of pieces of information has a similarity of at least equal to or greater than the predetermined similarity; determining a selecting number of information elements to be selected in each piece of information based on said rate; selecting said selecting number of information elements to be selected from each said piece of information according to priorities of the information elements applied in common to a group of pieces of information to be subjected to matching; and searching for pairs of pieces of information having no common selected information element between the pieces of information.