In an inference method using a rule, a rule condition part network and rule consequence part network are generated, an integral network of both the networks is used for inference. With this information method, the inference is performed at high speed by setting a shortcut arc so as to process the inference along the pattern matchable network portion. Further, use of the integral network of the rule condition and consequence parts enables not only forward and backward inferences but also a bidirectional inference with intimate couple between forward and backward inferences.