1. Method for preparing a recognition dictionary of decision tree structure, by which identification (classification) is effected, by the use of electronic data processing means while allocating each of a plurality of features prepared for objects to be recognized by recognition means to each of the nodes of a decision tree comprising (a) a step of estimating the maximum depth in representation of node level of the decision tree necessary for recognizing one of the objects to be recognized, (b) a step of estimating the sum of node numbers, which is the total sum of the depths in representation of node level of the decision tree necessary for recognizing all of the objects to be recognized, and (c) a step responsive to a requirement to said system of extracting (selecting) independently a feature, for which the maximum estimated depth according to said step (a) is the smallest, or a feature for which the sum of the estimated node numbers according to said step (b) is the smallest.