PURPOSE: To automatically adjust the membership function of a fuzzy control rule.

CONSTITUTION: The instruction is described in the language that is inputted by an operator 1 by making reference to the process measurement value and the display contents of a change contents display device 4. Then the instruction is sent to an instruction interpretation device 3 via an instruction input means 2 and then to an antecedent part membership function adjustment device 8 via an instruction conversion device 7. At the same time, the measurement value of a controlled system process 6 is sent to a controlled system process qualitative model storage 9 via a storage 5. The device 8 calculates the adjustment value of the antecedent part membership function of a fuzzy control rule storage 11 by making reference to the storage 9. This calculated adjustment value is confirmed by the operator 1, and the instruction showing a changeable state is inputted via a change propriety instruction device 10. Thus the antecedent part membership function of the storage 11 is changed.