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 feature values 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 each feature value and occurrence frequency of each feature value and for classifying the plurality of clusters into anyone of a plurality of classes, respectively, the plurality of classes including at least a class relating to a living mucosa and a class relating to a non-living mucosa; 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; a classification criterion calculation portion for calculating a criterion of classification when classifying the image included in at least one subset of the plurality of subsets into anyone 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 at least one subset; a classification portion for classifying each region in one image included in the at least one subset on the basis of the criterion of classification; and a lesion detection portion for carrying out processing to detect a lesion spot for each of the regions when the one image has a region classified as the class relating to the living mucosa on the basis of the classification result of the one image.