1. A method for automatically generating fuzzy reasoning rules which is performed by a controller apparatus, including the steps of: performing a fuzzy reasoning process based on rule parameters of membership functions constituting fuzzy reasoning rules representing relationships between input data and output data stored in a rule memory for storing rule parameters of membership functions constituting fuzzy reasoning rules and outputting results of said fuzzy reasoning process, each of said fuzzy reasoning rules being composed of antecedents and consequents; calculating a reasoning error and a change in the reasoning error to obtain a calculated reasoning error and a calculated change based on the results of said fuzzy reasoning process and said plurality of pairs of predetermined input and output data; adjusting said rule parameters of membership functions constituting said fuzzy reasoning rules stored in said rule memory, based on the results of said fuzzy reasoning process and a plurality of pairs of predetermined input and output data for said fuzzy reasoning process which are predetermined by a rule designer, when said calculated change is larger than a predetermined first threshold value; generating new rule parameters of membership functions constituting fuzzy reasoning rules and storing said new generated rule parameters of membership functions constituting said fuzzy reasoning rules in said rule memory, when said calculated change in the reasoning error is equal or smaller than said predetermined first threshold value; and alternately adjusting and generating rule parameters repeatedly until said calculated reasoning error is equal to or smaller than a predetermined second threshold value.