An image processing device includes: a step calculator configured to calculate, as a step, a difference in pixel values of pixels in a neighborhood with respect to each pixel in an image; a classifier configured to classify the pixels into classes for areas of the steps; a boundary ratio calculator configured to calculate, as a boundary ratio, a ratio of the number of pixels at a block boundary for each of the classes; and a block noise strength determinator configured to determine, as a block noise strength of the image, the step that is larger than a predetermined threshold and that is at a class having a largest value.