In an image processing device, in order to display an image on a display device having nonlinear gradation characteristics, first, a contrast estimation unit (37) estimates the contrast of the image represented by the image data (51) input from an image input device. Next, a luminance correction unit (38) subjects the pixel data constituting the image data (51) to a luminance conversion process on the basis of the estimated contrast and the gradation characteristics. Furthermore, the pixel data may sometimes be subjected to a sharpening process. The level of the sharpening performed for one or a plurality of character regions in the image represented by the image data (51) is higher than that for the pixel data of the pixels in remaining regions other than the character regions in the image. The image data (52) comprising the pixel data subjected to these processes is supplied to the display device. Therefore, the visibility of the image displayed on the display device can be improved.