1. An image processing device comprising: a level difference calculation means for calculating the difference of pixel values between each pixel and a neighborhood pixel as a level difference; a classification means for classifying respective pixels into classes in each range of the level difference; a boundary proportion calculation means for calculating proportion of the number of pixels at a block boundary as a boundary proportion according to the respective classes; and a block noise intensity determination means for determining a level difference of the class in which the boundary proportion is higher than a given threshold and is the maximum value as block noise intensity in the image.