Thesauruses meeting users' purposes are generated by various operations as required. A plurality of external thesauruses 2 each storing a thesaurus to be retrieved are connected to a thesaurus retrieval and synthesis device 3 through a network 1, wherein the thesaurus retrieval and synthesis device 3, on receiving a request to define the thesauruses to be synthesized from an input unit 5, retrieves partial thesauruses corresponding to the request from the external thesauruses 2 in a retrieval unit 32. A synthesis unit 33 forms a new thesaurus from a plurality of retrieved partial thesauruses by subjecting them to product, addition, and other operations corresponding to the request.