Provided is an intra prediction decoding apparatus that restores quantized residual coefficients, intra prediction information and size information on a prediction unit from a received bit stream, restores an intra prediction mode of the current prediction unit on the basis of the intra prediction information and the size information on the current prediction unit, generates unavailable reference pixels of the prediction unit, and adaptively filters the reference pixels on the basis of the intra prediction mode. Also, the apparatus generates a prediction block by adaptively filtering reference pixels corresponding to the intra prediction mode. Then, the apparatus generates a restoration image using the prediction block and a restored residual block. Accordingly, a prediction block close to an original image can be restored, and an image compression ratio can be improved.