1. A knowledge acquisition support system in an expert system, comprising: a case data storage means for storing data of cases including a set of plural pieces of data items and conclusions; a relational expression storage means connected to said case data storage means for storing relational expressions prescribing relations of said plural pieces of data items; a case preprocessing part for analyzing said data of cases stored in said case data storage means for performing one of deleting data of ones of said cases which do not satisfy a predetermined evaluation criterion and changing said data of said ones of said cases to satisfy the criterion including storing said changed data in said case data storage means; a rule generation part for generating rules by determining from said data of cases whether predetermined relations exist between at least one predetermined one of the data items and a predetermined one of the conclusions and classifying said predetermined relations of said cases preprocessed by said case preprocessing part with reference to said relational expressions stored in said relational expression storage means; a rule storage means for storing said rules generated by said rule generation part; a test data storage means for storing data of tests used for evaluating said rules generated by said rule generation part; a rule evaluation part connected to said test data storage means and said rule storage means for evaluating said rules generated by said rule generation part by use of said test data stored in said test data storage means; and an information indication part for indicating evaluated results of said rule evaluation part.