An image processing device includes a generation unit and a smoothing processor. The generation unit calculates an edge strength on the basis of a stairs tone strength indicative of differences between a first parameter and a second parameter. The first parameter is a first gradient based on pixel values of a pixel of interest in an input image and adjacent pixels included in a first range with respect to the pixel of interest. The second parameter is one of a variance based on pixel values of the pixel of interest and the adjacent pixels, and a second gradient based on the pixel value of the pixel of interest and adjacent pixels included in a second range. The smoothing processor performs a nonlinear smoothing operation on the pixel value of the pixel of interest and the adjacent pixels included in the first range on the basis of the calculated edge strength.