To reduce an volume of index information in a whole sentence retrieval to save a storage resource, in a storage system provided with a de-duplication function and a whole sentence retrieval function.

This system is provided, in a storage device 100, with a processing part 501 for de-duplicating a plurality of files having the same content, as to a file group of data input and output into/from a host device 400. A whole sentence retrieval processing server 200 is provided for conducting whole sentence retrieval processing in the file group, and is provided with a processing part 502 for making the whole sentence retrieval processing correspond to the de-duplication. Index information preparation processing by a whole sentence retrieval processing part is restrained as to the plurality of objective files having the same content, in response to a de-depulication situation of the file group. The volume of the index information is reduced by this manner.