A search server for which data stored in a hierarchical control server utilizing a plurality of storage devices is the object of a search, wherein the search server is designed to update a search index to data while the data exists in an upper-hierarchy storage of the hierarchical control server. Included in a computer system are: a storage unit for storing the usage status of an upper-hierarchy storage area of a hierarchical storage having the upper-hierarchy storage area and a lower-hierarchy storage area; and a determination unit for determining, according to the stored usage status, which process should be given priority between an indexing process for data that is an index-updating candidate among data stored in the hierarchical storage, or a migration process for moving the data to the lower-hierarchy storage area.