To provide an effective factor extraction system in which samples are generated artificially from a sample group and a virtual sample set is created so that even when the number of sample is relatively small, specific factors can be selected/extracted with high reliability by using the virtual sample set. The effective factor extraction system comprises a section for extracting samples arbitrarily from sample sets and creating a plurality of paired virtual sample sets, a statistical quantity operating section for reading out the feature value held by sample contained in respective virtual sample sets and operating the average value and the variance, a section for operating Fisher ratio from the average value and the variance, and a section for testing significant factors using the operated Fisher ratio.