1 ) A classification factor detection apparatus which detects, with respect to the results of classification into two groups of a plurality of objects each constituted by a plurality of constituents through analysis as to whether or not each object has a predetermined characteristic, a set of some of the constituents as a factor of the classification, said apparatus comprising: first selection means of selecting a first pattern which is a set of at least one of the plurality of constituents of one of the plurality of objects; second selection means of selecting, from the plurality of constituents in one of the plurality of objects, a second pattern formed of the first pattern and at least one of the constituents added to the first pattern; evaluation value generation means of generating an evaluation value for a measure of classification of the plurality of objects under a classification condition including the first pattern but not including the second pattern on the basis of the number of objects satisfying the classification condition in the plurality of objects classified into the first group and the number of objects satisfying the classification condition in the objects classified into the second group; and classification factor output means of outputting the constituents in each of the first pattern and the second pattern as a factor of classification when the measure indicated by the evaluation value exceeds a reference measure determined in advance.