An apparatus and method for correcting the sharpness of an image signal, using a Haar Wavelet transform and a difference between pixel values adjacent to the edge of the image signal to be corrected while reducing the occurrence of overshoot and undershoot at the edge of the image signal, are provided. The apparatus includes an edge detector for detecting data on the edge of the image signal, by performing a multi-stage Haar Wavelet transform on the image signal, a gain detector for detecting a gain for correcting the image edge, a pixel value detector for detecting a corrected pixel value regarding the edge data at a position to be corrected by performing an operation on the edge data, at least one pixel adjacent to the edge data, and the gain, and an image signal generator for generating an image whose edge is formed based on the corrected pixels.