PURPOSE: To enable a range of a typical value of a characteristic amount of each target type to be assumed to be set with a boundary in an ambiguous form and further a target type to be classified by evaluating ambiguity of this prior information based on an actual target value of the amount of characteristic.

CONSTITUTION: A range of a typical value of a characteristic amount is expressed via a conformity degree which ranges from 0 to 1 and at the same time the degree where each condition satisfies is evaluated by this conformity degree regarding a plurality of characteristic amount. Furthermore, the degree where an entire rule is realized is evaluated by a value which is obtained by uniting these plurality of conformity degrees with an average operation and a target type is classified by a criterion using a threshold for this united value.