1. A file list generation method, comprising the steps of: storing index information created about search target files into a first storage area; determining a dividing policy to divide a scan target directory scanning operation to be performed with a distributed server cluster, by acquiring directory URLs of the search target files from the index information stored in the first storage area, and counting the number of directories in each layer through analysis of the directory URLs, the scan target directory scanning operation being divided based on the result of the counting; dividing directories of the search target files in accordance with the determined dividing policy; acquiring a snapshot of a current directory tree of scan target files, and storing the snapshot into a second storage area; scanning, in a distributed manner, the search target files in respective directories in the snapshot of the current directory tree and a snapshot of a directory tree of search target files acquired prior to the determination of the divided policy and stored in a third storage area, the scanning being performed with the distributed server cluster on the basis of division units determined in the determining the dividing policy; and comparing the results of the distributed scans, and creating and outputting a list of files that are added, deleted, or changed after the creation of the index information.