An apparatus of decoding a video, comprising: a parser configured to: obtain, from a bitstream, a most probable mode flag indicating whether one of candidate intra prediction modes is used to determine an intra prediction mode of a current block, and parse, from the bitstream, a mode index indicating one among candidate intra prediction modes included in a candidate list, when the most probable mode flag indicates that one of the candidate intra prediction modes is used; a candidate list determiner configured to determine a fixed number of the candidate intra prediction modes in the candidate list according to intra prediction modes of a left block and an upper block; and an intra prediction performer configured to perform intra prediction on the current block using a prediction mode, indicated by the mode index, among the candidate intra prediction modes included in the candidate list. wherein, the candidate list determiner determines the candidate intra prediction modes to include a planar mode, when the intra prediction modes of the left block and the upper block are equal to each other and the intra mode of the left block is the DC mode. a parser configured to: obtain, from a bitstream, a most probable mode flag indicating whether one of candidate intra prediction modes is used to determine an intra prediction mode of a current block, and parse, from the bitstream, a mode index indicating one among candidate intra prediction modes included in a candidate list, when the most probable mode flag indicates that one of the candidate intra prediction modes is used; a candidate list determiner configured to determine a fixed number of the candidate intra prediction modes in the candidate list according to intra prediction modes of a left block and an upper block; and an intra prediction performer configured to perform intra prediction on the current block using a prediction mode, indicated by the mode index, among the candidate intra prediction modes included in the candidate list. wherein, the candidate list determiner determines the candidate intra prediction modes to include a planar mode, when the intra prediction modes of the left block and the upper block are equal to each other and the intra mode of the left block is the DC mode. obtain, from a bitstream, a most probable mode flag indicating whether one of candidate intra prediction modes is used to determine an intra prediction mode of a current block, and parse, from the bitstream, a mode index indicating one among candidate intra prediction modes included in a candidate list, when the most probable mode flag indicates that one of the candidate intra prediction modes is used; a candidate list determiner configured to determine a fixed number of the candidate intra prediction modes in the candidate list according to intra prediction modes of a left block and an upper block; and an intra prediction performer configured to perform intra prediction on the current block using a prediction mode, indicated by the mode index, among the candidate intra prediction modes included in the candidate list. wherein, the candidate list determiner determines the candidate intra prediction modes to include a planar mode, when the intra prediction modes of the left block and the upper block are equal to each other and the intra mode of the left block is the DC mode.