PURPOSE: To omit the useless repetition of evaluation of the elements of the antecedent part of a fuzzy rule and to improve the fuzzy inference efficiency by evaluating previously all elements forming the antecedent part and carrying out an inference by reference to the results of evaluation of the elements forming the antecedent part.

CONSTITUTION: A fuzzy inference module 6 evaluates the input value of the variable corresponding to a fuzzy gathering stored in an antecedent part fuzzy gathering storage area 3 and stores the result of the evaluation in an evaluation result store part. When the result of evaluation is stored in an entire store part, the module 6 evaluates the fuzzy rule stored in a fuzzy rule storage area 5. When all fuzzy rules stored in the area 5 are evaluated and the conclusions of these evaluation results are obtained, the final one of these conclusions is obtained by an arithmetic operation and outputted. Thus it is possible to omit the useless repetion of evaluation for the elements of the antecedent part and to effectively perform an inference.