1. A document retrieval system which searches a target document to be retrieved in response to a retrieval request and ranks a retrieval result, said system retaining index information for each of a plurality of fields of said target document and comprising: a field rate inputting means for allowing the user to specify a rate of influence of a field on a ranking of said retrieval result, and for allowing the user to specify said rate of influence of any field on the ranking of said retrieval result.