A method of decoding an intra prediction mode, comprising: reconstructing an intra prediction mode group indicator and a prediction mode index; constructing an MPM group including three intra prediction modes using valid intra prediction modes of left and top blocks of a current block; determining an intra prediction mode of the MPM group corresponding to the prediction mode index as an intra prediction mode of the current block when the intra prediction mode group indicator indicates the MPM group; and determining the intra prediction mode of the current block using the prediction mode index and the three intra prediction modes of the MPM group when the intra prediction mode group indicator does not indicate the MPM group; wherein non-directional intra prediction modes are a DC mode and a planar mode, and a mode number of the planar mode is lowest, wherein when the intra prediction modes of the left and top blocks of the current block are not equal to each other and none of the intra prediction modes of the left and top blocks is equal to the planar mode, the MPM group includes the intra prediction modes of the left and top blocks and the planar mode, wherein when the intra prediction modes of the left and top blocks of the current block are equal to each other and the intra prediction mode of the left block is one of the two non-directional intra prediction modes, the MPM group includes the DC mode, the planar mode and a vertical mode, and wherein when the intra prediction modes of the left and top blocks of the current block are valid and equal to each other and the intra prediction mode of the left block is one of directional intra prediction modes, the MPM group includes the intra prediction mode of the left block and two directional intra prediction modes. reconstructing an intra prediction mode group indicator and a prediction mode index; constructing an MPM group including three intra prediction modes using valid intra prediction modes of left and top blocks of a current block; determining an intra prediction mode of the MPM group corresponding to the prediction mode index as an intra prediction mode of the current block when the intra prediction mode group indicator indicates the MPM group; and determining the intra prediction mode of the current block using the prediction mode index and the three intra prediction modes of the MPM group when the intra prediction mode group indicator does not indicate the MPM group; wherein non-directional intra prediction modes are a DC mode and a planar mode, and a mode number of the planar mode is lowest, wherein when the intra prediction modes of the left and top blocks of the current block are not equal to each other and none of the intra prediction modes of the left and top blocks is equal to the planar mode, the MPM group includes the intra prediction modes of the left and top blocks and the planar mode, wherein when the intra prediction modes of the left and top blocks of the current block are equal to each other and the intra prediction mode of the left block is one of the two non-directional intra prediction modes, the MPM group includes the DC mode, the planar mode and a vertical mode, and wherein when the intra prediction modes of the left and top blocks of the current block are valid and equal to each other and the intra prediction mode of the left block is one of directional intra prediction modes, the MPM group includes the intra prediction mode of the left block and two directional intra prediction modes. <EOS>