Abstract: In a bit string check method, a bit string to be searched is divided into a plurality of partial-object bit strings, which are compared to the plurality of registration bit patterns at multiple stages. At a current stage which is one of the multiple check-stages, comparison is made with all the possible values of a partial-object bit string in accordance with the comparison result and the pattern table where a plural registration bit pattern is registered, it is possible to obtain a judgment result indicating a presence or absence of a partial registration bit pattern which matches at least the partial-object bit string. According to the judgment result, check-continuation information including the address of the pattern table of the stage subsequent to the current stage is outputted.