PURPOSE: To shorten the condition discriminating processing time to increase the inference processing speed by converting a knowledge source to an execution and condition discriminating processing program so as to collectively execute the executing action and an extracted condition discriminating processing.

CONSTITUTION: A rule compiler 2 beforehand converts a knowledge source 1 to an execution and condition discriminating processing program 3 in accordance with prescribed procedures. That is, all condition elements of rules affected by execution of action parts of rules are listed up, and the executing action and listed-up condition elements are converted to a procedural program, and each processing is performed for executing action parts of all rules. At the time of actual inference execution, an inference control part 4 determines the rule to be first executed and next executes the execution and condition discriminating processing program of the corresponding rule. That is, the knowledge source 1 is beforehand converted to the execution and discrimination processing program in accordance with prescribed procedures by a rule compiler 2, and thereby, wasteful condition discrimination and processing at the time of inference execution are eliminated to increase the inference processing speed.