The present invention provides a classifying method of classifying an article into one of a plurality of groups based on an image of the article, comprising determining an evaluation method for obtaining an evaluation value of an image by using at least some of sample images, obtaining evaluation values for the sample images by the determined evaluation method, changing a group to which a sample of at least one sample image having a singular evaluation value among the sample images belongs, changing the evaluation method using the sample images after changing the group to which the sample of the at least one sample image belongs, obtaining an evaluation value for the image of the article using the changed evaluation method, and classifying the article into one of the plurality of groups based on the evaluation value for the image of the article.