PURPOSE: To set the membership function of a complicated shape without increasing the capacity of a memory by storing fundamental pattern data in a first storage means, and storing a parameter for showing the combination of the fundamental pattern data in a second storage means.

CONSTITUTION: The device is provided with a memory 11 for storing a membership function parameter, a memory 12 for storing a fundamental pattern, and a rule memory 13 for storing If/then rules. In such a state, plural kinds of fundamental pattern data to which a grade is given when a variable is given are stored in advance in the fundamental pattern memory 12. Also, such a parameter for showing the combination of plural pieces of fundamental patterns as a grade of a membership function having a prescribed shape is obtained by giving a grade obtained by giving a variable to one fundamental pattern data as a variable of the other fundamental pattern data is stored in advance in the membership function parameter memory 11.