PURPOSE: To improve the processing speed of the expert system as to a system which generates a procedure type inference processing the basis of a previous execution history for the inference processing of the expert system.

CONSTITUTION: Input data 4 are checked by the procedure type inference processing 2; when there is a corresponding inference result, the result is displayed at a display part 5 or outputted to an output part 7, but when not, inference is performed by an inference engine 3 and knowledge base 8 and the inference result is displayed at the display part 5 or outputted to the output part 7. The inference result is extracted by inference result extraction 13 by using a knowledge base execution history file 10 and a conviction degree calculation history file 11 and the procedure type inference processing is generated by procedure type inference processing generation 14 by using the extracted inference result and an input data history file 9 and used as a procedure type inference process 2 at the time of next expert system execution to improve the processing speed of the expert system.