PURPOSE: To simultaneously output grades of plural kinds of membership function at the time of giving one input by providing a Z function circuit, an S function circuit, an inverting circuit, and a MIN circuit.

CONSTITUTION: An output Vs of an S function circuit 20 is given to an inverting circuit 30A and a MIN circuit 40, and an output VZ of a Z function circuit 10 is given to an inverting circuit 30B and the MIN circuit 40. The output of the inverting circuit 30A expresses a function value (grade) αNE of a membership function NE, and the output of the inverting circuit 30B expresses a function value (grade) αPO of a membership function PO. The MIN circuit 40 outputs smaller one of the output value of the S function circuit 20 and the output value of the Z function circuit 10, and the output expresses a function value (grade) αZR of a membership function ZR. Thus, grades of plural kinds of membership function are outputted when one input variable is given.