1. An information retrieving system comprising: a database in which a keyword and an attribute of the keyword are stored together with a document ID for discriminating a source document; a retrieval key input section which captures at least one keyword and/or retrieval key constituted by attribute information which is not specified as a keyword; a retrieval section which retrieves information from the database on the basis of the keyword and/or the attribute of the attribute information captured by the retrieval key input section; and an output section which outputs a retrieval result obtained by the retrieval section.