Abstract: A firewall device comprises a storage unit that stores therein one or more rules related to blocking a request for each of a plurality of WEB servers independently of the rule for another WEB server; a feature-amount calculating unit that calculates a feature amount for each of the WEB servers based on a number of detections with regard to each index in each of the WEB servers; and a rule updating unit that updates a rule stored in the storage unit for each of the WEB servers based on the feature amount calculated by the feature-amount calculating unit.