An image decoding apparatus comprising: a parsing module for decoding intra prediction information from a received bit stream; an intra prediction mode decoding module for decoding an intra prediction mode of a current prediction unit using the intra prediction information and an MPM group including three intra prediction modes; a reference pixel creating module for creating a reference pixel when at least one of reference pixels is not valid; a reference pixel filtering module for filtering reference pixels depending on a size of a prediction block and the intra prediction mode; and a prediction block creating module for creating a prediction block using the intra prediction mode, wherein the intra prediction information includes a prediction mode group indicator and a prediction mode index, and the decoding method of the prediction mode index varies depending on the prediction mode group indicator, and wherein the prediction mode group indicator indicates whether the MPM group includes the intra prediction mode of the current prediction unit or not, and the prediction mode index indicates the intra prediction mode of the current prediction unit among the three intra prediction modes of the MPM group when the prediction mode group indicator indicates that the MPM group includes the intra prediction mode of the current prediction unit, characterised in that the MPM group includes intra prediction modes of a left and a top blocks of the current prediction unit and planar mode when the intra prediction modes of the left and the top blocks are not equal to each other and are directional intra prediction modes, and when both of the intra prediction modes of the left and top blocks are not present, the MPM group consists of planar mode, DC mode and vertical mode. a parsing module for decoding intra prediction information from a received bit stream; an intra prediction mode decoding module for decoding an intra prediction mode of a current prediction unit using the intra prediction information and an MPM group including three intra prediction modes; a reference pixel creating module for creating a reference pixel when at least one of reference pixels is not valid; a reference pixel filtering module for filtering reference pixels depending on a size of a prediction block and the intra prediction mode; and a prediction block creating module for creating a prediction block using the intra prediction mode, wherein the intra prediction information includes a prediction mode group indicator and a prediction mode index, and the decoding method of the prediction mode index varies depending on the prediction mode group indicator, and wherein the prediction mode group indicator indicates whether the MPM group includes the intra prediction mode of the current prediction unit or not, and the prediction mode index indicates the intra prediction mode of the current prediction unit among the three intra prediction modes of the MPM group when the prediction mode group indicator indicates that the MPM group includes the intra prediction mode of the current prediction unit, the MPM group includes intra prediction modes of a left and a top blocks of the current prediction unit and planar mode when the intra prediction modes of the left and the top blocks are not equal to each other and are directional intra prediction modes, and when both of the intra prediction modes of the left and top blocks are not present, the MPM group consists of planar mode, DC mode and vertical mode.