A video decoding method according to this document includes deriving a first candidate intra prediction mode based on a first neighboring block located on a left side of a current block, deriving a second candidate intra prediction mode based on a second neighboring block located on an upper side of the current block, constructing a most probable mode (MPM) list for the current block based on the first candidate intra prediction mode and the second candidate intra prediction mode, deriving an intra prediction mode for the current block based on the MPM list, generating predicted samples by performing prediction for the current block based on the intra prediction mode, and generating a reconstructed picture for the current block based on the predicted samples.