A system includes a unit to generate a set of free itemsets with a frequency in a database greater than or equal to a threshold value, a unit to generate a rule candidate with, a conditional part set to the free itemset α, and a consequent part set to an item x not sharing an attribute with the free itemset, and finds a set of attributes of an antecedent part of the rule by depth first search, the attribute not included in neither α nor x, a unit to collate the rule to the database to judge validity of the rule, and a unit to check for minimality of the rule decided to be valid to output the rule when the rule is minimal.