1. An image processing apparatus, comprising: a filter for performing an iterative filtering on an input image; and an iterative filtering stopping device for determining whether to stop the iterative filtering based on a filtered image obtained from each iteration of the iterative filtering with increasing of iteration times, wherein the iterative filtering stopping device comprises: a noise image acquisition unit for evaluating, after the filter completes each iteration, a noise image according to the filtered image obtained from the iteration and the input image; a correlation acquisition unit for evaluating a correlation between the noise image and the filtered image; and a stopping determination unit for calculating a feature value representing decreasing speed of the correlation during the iterative filtering process, determine whether a predetermined relation is met between the feature value and a predetermined threshold, and stop the iterative filtering if the predetermined relation is met between the feature value and the predetermined threshold.