1. An image-processing device applying a predetermined process to input image data so as to output the processed image data, the image-processing device comprising: a medium-density detection unit detecting a medium-density field of an image represented by said image data; an expansion unit applying an expansion process to said medium-density field detected by said medium-density detection unit; and a non-character edge judgment unit judging said medium-density field applied with said expansion process by said expansion unit as a non-character edge field of said image represented by said image data.