Provided is an apparatus for improving the sharpness of an image. The apparatus includes an edge detector, an effective edge judging unit, an effective edge classifying unit, an isolated edge judging unit, and a 2-D HPF applying unit. The edge detector calculates an edge value using brightness relation with neighboring pixels with respect to each of pixels of an input image. The effective edge judging unit determines effective edge pixels. The effective edge classifying unit determines weak edge pixels and strong edge pixels. The isolated edge judging unit judges an isolated edge pixel included in an isolated edge. The 2-D HPF applying unit applies a first 2-D HPF to the weak edge pixels, and applies a second 2-D HPF to the strong edge pixels to generate edge strengthening values. The edge strengthening value applying unit adds the edge strengthening values to brightness values of the respective pixels of the input image.