PURPOSE: To exactly grasp even small contradiction and investigate its cause. and corrects an inference rule and maintain highly precise control by providing a self-diagnosing function which checks contradiction between the arithmetic result of an antecedent arithmetic part and the arithmetic result of a consequent arithmetic.

CONSTITUTION: One input value is inputted from a controlled system through an input interface 14 and stored in an input value main memory 17a. Then an antecedent arithmetic program 13c is started to read out the membership function 16a corresponding to the input value and the input conviction degree (grade). Then inference arithmetic for an event belonging to each input conviction degree is performed by using plural inference rules 16a. After the antecedent arithmetic processing, a consequent arithmetic processing program 13d is started to integrate previously found output characteristics as to general physical quantities, calculation a physical manipulated variable. After the consequent processing is thus completed, a contradiction finding self-diagnostic program 13b is started to check the contradiction of the physical manipulated variable.