1. A fuzzy inference apparatus comprising: an input device for entering input data relating to phenomena; a storage device for storing knowledge of expert users expressing relationships between phenomena and conclusions as a plurality of membership functions; a grade calculating device for determining a grade measure for said input date with respect to each of said plurality of membership functions stored in said storage device; a fuzzy information amount calculating device for calculating a fuzzy information amount for each phenomenon using said grade measures; a relational coefficient calculating device for calculating a relational coefficient for each conclusion which expresses the relatedness of multiple of said phenomena and said conclusion using said grade measures; and a possibility calculating device for performing fuzzy inferences on said phenomena to determine a possibility of a conclusion using said grade measures, said fuzzy information amounts and said relational coefficients.