Abstract: Documents, which have typically been searched for using multiple search engines based on the access rights of multiple accounts on multiple authentication servers, are searched for using a single federated search engine via a single log in. A host system having an account correspondence database is provided with a function of re-indexing indexes that have been individually created with multiple search engines, so that indexes of all of the search engines are created in advance. When a search is requested, correspondence information is read from the account correspondence database, so that a document search involving the use of only the host system is executed based on all of the relevant account rights.