An image decoding apparatus comprising: a parsing unit for decoding intra prediction information from a received bit stream; an intra prediction mode decoding unit 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; and a prediction block creating unit 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, wherein the prediction mode group indicator indicates whether the intra prediction mode of the current prediction unit belongs to the MPM group or not, and an intra prediction mode in the MPM group corresponding to the prediction mode index is set as the intra prediction mode of the current prediction unit when the prediction mode group indicator indicates MPM group, a size of the prediction block is determined according to transform information, the three intra prediction modes are determined according to intra prediction modes of left and top blocks of the current prediction unit, when only one of the intra prediction modes of left and top blocks of the current prediction unit is available, two additional intra prediction modes are added to the MPM group, characterised in that the decoding apparatus is configured to determine the three intra prediction modes such that: when the intra prediction mode of the left block is equal to the intra prediction mode of the top block and the intra prediction mode of the left block is a DC mode, the MPM group includes a planar mode, the DC mode and a vertical mode. a parsing unit for decoding intra prediction information from a received bit stream; an intra prediction mode decoding unit 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; and a prediction block creating unit 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, wherein the prediction mode group indicator indicates whether the intra prediction mode of the current prediction unit belongs to the MPM group or not, and an intra prediction mode in the MPM group corresponding to the prediction mode index is set as the intra prediction mode of the current prediction unit when the prediction mode group indicator indicates MPM group, a size of the prediction block is determined according to transform information, the three intra prediction modes are determined according to intra prediction modes of left and top blocks of the current prediction unit, when only one of the intra prediction modes of left and top blocks of the current prediction unit is available, two additional intra prediction modes are added to the MPM group, characterised in that the decoding apparatus is configured to determine the three intra prediction modes such that: when the intra prediction mode of the left block is equal to the intra prediction mode of the top block and the intra prediction mode of the left block is a DC mode, the MPM group includes a planar mode, the DC mode and a vertical mode.