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 in 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 when only one of intra prediction modes of the left and top blocks of the current block is valid, two additional intra prediction modes are included in the MPM group and the two additional intra prediction modes are determined based on the valid intra prediction mode, 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 a 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 valid and equal to each other and the intra prediction mode of the left block is one of the directional intra prediction modes, two directional intra prediction modes are added to the MPM group, 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 a DC mode, the MPM group includes the DC mode, the planar mode and a vertical mode, wherein the intra prediction mode group indicator indicates whether the intra prediction mode of the current block belongs to the MPM group or to a group other than the MPM group, and the prediction mode index indicates a specific intra prediction mode in the MPM group or in the group other than the MPM group; and wherein the planar mode and the DC mode are non-directional intra modes and the mode number of the planar mode is lower than other 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 in 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 when only one of intra prediction modes of the left and top blocks of the current block is valid, two additional intra prediction modes are included in the MPM group and the two additional intra prediction modes are determined based on the valid intra prediction mode, 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 a 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 valid and equal to each other and the intra prediction mode of the left block is one of the directional intra prediction modes, two directional intra prediction modes are added to the MPM group, 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 a DC mode, the MPM group includes the DC mode, the planar mode and a vertical mode, wherein the intra prediction mode group indicator indicates whether the intra prediction mode of the current block belongs to the MPM group or to a group other than the MPM group, and the prediction mode index indicates a specific intra prediction mode in the MPM group or in the group other than the MPM group; and wherein the planar mode and the DC mode are non-directional intra modes and the mode number of the planar mode is lower than other intra prediction modes.