1. A digital fuzzy inference system having a plurality of fuzzy rules comprising: means for inputting at least two binary data; means for inputting parameters for an if-part membership function represented by a line having a combination of gradients, each parameter including a tangent of a gradient and a point of change at which the gradient of the line changes, and each parameter being input for each of the fuzzy rules and each of the binary data; means for producing if-part membership values corresponding to the binary data in accordance with the parameters inputted by said parameters inputting means; means for obtaining a minimum value of the if-part membership values for each of the fuzzy rules; means for obtaining an inferential result in accordance with the minimum value for each of the fuzzy rules; and means for obtaining a center of gravity of inferential results for all the fuzzy rules.