A computer-implemented extraction method characterized by comprising: A) storing first information and second information into a storage unit, the first information including a plurality of presence information for each of a plurality of files, respectively, each of the plurality of presence information indicating presence information for a specific plurality of character data, respectively, for each of the plurality of files, the second information indicating for each of the specific plurality of character data, respectively, whether at least any one of the plurality of files includes the specific plurality of character data; B) updating the first information and the second information with addition of an additional file to the plurality of files, the first information being updated by merging additional presence information that indicates whether the additional file includes each of the specific plurality of character data, the second information being updated to indicate whether the portion of the plurality of files to which the additional file is added includes the specific plurality of character data, using the additional presence information; and C) extracting from the portion of the plurality of files corresponding to the second information, one or more files that include a specific character data among the specific plurality of character data based on the first information, when a search request is accepted for the specific character data among the specific plurality of character data and the second information is detected to include the specific character data among the specific plurality of character data. A) storing first information and second information into a storage unit, the first information including a plurality of presence information for each of a plurality of files, respectively, each of the plurality of presence information indicating presence information for a specific plurality of character data, respectively, for each of the plurality of files, the second information indicating for each of the specific plurality of character data, respectively, whether at least any one of the plurality of files includes the specific plurality of character data; B) updating the first information and the second information with addition of an additional file to the plurality of files, the first information being updated by merging additional presence information that indicates whether the additional file includes each of the specific plurality of character data, the second information being updated to indicate whether the portion of the plurality of files to which the additional file is added includes the specific plurality of character data, using the additional presence information; and C) extracting from the portion of the plurality of files corresponding to the second information, one or more files that include a specific character data among the specific plurality of character data based on the first information, when a search request is accepted for the specific character data among the specific plurality of character data and the second information is detected to include the specific character data among the specific plurality of character data.