1. An image processing device comprising: an image signal input portion for inputting an image signal on the basis of a plurality of images obtained by medical equipment having an imaging function; an image dividing portion for dividing the plurality of images into a plurality of regions, respectively, on the basis of the image signal inputted in the image signal input portion; a feature value calculation portion for calculating one or more features value in each of the plurality of regions divided by the image dividing portion; a cluster classifying portion for generating a plurality of clusters in a feature space on the basis of the feature value and occurrence frequency of the feature value and for classifying the plurality of clusters into any one of a plurality of classes, respectively; a subset generation portion for generating a plurality of subsets on the basis of imaging timing of each of the plurality of images using the plurality of images; and a classification criterion calculation portion for calculating a criterion of classification when classifying the image included in the one subset into any one of the plurality of classes on the basis of the distribution state of the feature value in the feature space of each image included in the one subset generated by the subset generation portion.