The end of a communication period can be detected reliably and efficiently by a control unit and validity/invalidity of search rules in a search table can be effectively managed. A timer is provided so as to correspond to each entry area of the search table. Then, under control of a timer managing unit, the timer starts a counting operation whenever information is written in a validity management table or a packet in which a communication parameter matches a packet search condition corresponding to information on the validity management table that is set as valid is received. In addition, when a counting time of the timer exceeds a preset time-out time, information indicating the time-out is stored in a time-out management table.