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 in a time series 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; an image region classifying portion for classifying each of regions into any one of a plurality of classes on the basis of the feature value; a representative value calculation portion for calculating a representative value of the feature value of at least one class in each of the plurality of images; a smoothing portion for applying smoothing in a time direction along the time series to each of the representative value; a variation detection portion for detecting variation in the representative value in the time series and detecting a time zone or an image in which the variation in the representative value becomes locally large on the basis of the representative value applied with the smoothing by smoothing portion; and a determining portion for determining that a lesion has been imaged in the time zone or the image, or determining that an imaged portion that has changed in the time zone or the image, when it is detected that the time zone or the image, in which the variation in the representative value becomes locally large, is present only in any one of the plurality of classes.