Abstract: In a learning method, training data and verification data each including a set of input and output values are taken as teacher data, and a change of an error between an output value calculated by use of the input data of the verification data and the output value of the verification data and a change of an error between an output value calculated by use of the input value of the training data and the output value of the training data are simultaneously displayed, thereby preventing an overlearning and reducing the number of times of learning. Also in the learning method, fuzzy knowledge data is inputted and displayed, a range of the object of learning is interactively designated from among the displayed fuzzy knowledge, and a learning is made on the basis of a predetermined learning algorithm to change the fuzzy knowledge in the designated range, thereby performing the learning of a fuzzy knowledge with a user's intention reflected.