Filtering system and filtering method

In Web servers with access controlled objects, access control refusals may be erroneously recognized as caused by DOS attacks. A filtering device (20) according to the invention filters HTTP communication between a client device (30) and a Web server device (50). The filtering device (20) performs access control based on the URL. If determination result is an access refusal, the TCP termination process is performed. The filtering device has detection unit of frequent accesses to access control object data in the same Web server device (50) from the same client device (10) and a disconnect unit of a TCP connection to the Web server device (50) after detection through the detection unit.