PURPOSE: To verify an inference knowledge and to easily set and correct the inference knowledge by detecting the area where the membership value is smaller than a membership function deficiency detection threshold.

CONSTITUTION: When rule verification is requested from an inference knowledge setting means 6, a rule verifying means 7 first verifies membership functions. Since an area where rules are not defined yet exist if the area where the membership function is not set for a certain input variable, it is verified that membership functions used by the fuzzy rule are defined in the overall area in the input range. In this case, the membership function deficiency detection threshold is set, and the definition area of an input variable is scanned to obtain the membership value at this time, and the membership function is not set for the input variable in the area where this value is smaller than the threshold. This processing is performed for all input variables to detect area where membership functions are deficient.