PURPOSE: To shorten the processing time at the time of preparing a code book for setting a set of patterns for representing each category.

CONSTITUTION: First of all, a first vector (× mark) is set as a code book vector, and a circle of certain size (a) is considered. Subsequently, a second vector ( mark) is presented, and when a second vector is contained in the circle of the code book vector (× mark), a category B of a second vector is added to a category A represented by its code book vector. In the case a second vector is not contained, it becomes a code book vector of each different category A and B. The presentation is repeated until all vectors are finished, and each time, whether the presented vector is contained in the circle which becomes the code book vector already or not is decided.