PURPOSE: To evaluate a fuzzy rule without evaluating again the elements forming the antecedent part of the fuzzy rule by using the flag information showing whether these component elements are evaluated or not.

CONSTITUTION: An evaluation flag store part of an antecedent part fuzzy gathering storage area 3 judges whether the variables forming the antecedent part of a fuzzy rule are evaluated or not. If so, the second evaluation is omitted and the reference is applied to the result of evaluation stored in a membership function storage part. If not, those variables are evaluated and the result of evaluation is stored together with the flag information showing the end of evaluation. Then the due processing is carried on. The consequent part of the fuzzy rule is evaluated based on the result of evaluation of the variable of the antecedent part. The result of evalation of the consequent part is stored in a consequent part fuzzy gathering storage area 4. Thus the fuzzy inference efficiency is improved with no useless processing carried out.