PURPOSE: To improve an inference speed even when there are many fuzzy rules or the like.

CONSTITUTION: In a fuzzy inference system for judging the sort (earthquake or no) of an oscillation waveform by inputting six feature variables to an inference part 10 and executing fuzzy inference, the inference part 10 is provided with a rule storing part 11, an MF storing part 12 and an inference execution part 13 for executing fuzzy inference by inputting applied feature variables. The rule storing part 11 stores rule groups grouped based upon labels indicating the numbers of pulses which ice one of the feature values. The number of pulses is divided into crisps by a multicomparator 20, labels for respective crisps are determined and then inputted to a rule selection part 14 in the inference part 10. The selecting part 14 selects a rule group relating to labels equal to the determined and applied label and a rule group which does not have the number of pulses in its condition part and sends the selected rule groups to the inference execution part 13. Since rules to be used for inference are a part of stored rules and only the small number of rules is used for the inference, thereby processing can be enabled at high speed.