An image decoding method includes: configuring a MPM list including candidate intra prediction modes for a current block; deriving an intra prediction mode of the current block from the MPM list on the basis of MPM index information indicating an intra prediction mode, among the candidate intra prediction modes included in the MPM list, for the current block; generating prediction samples for the current block on the basis of the intra prediction mode; and generating a reconstructed picture for the current block on the basis of the prediction samples, wherein the step for configuring the MPM list comprises, on the basis of the case where the value of reference line index information, representing a reference line used for the intra prediction of the current block, is not zero, deriving a DC mode as one mode among the candidate intra prediction modes, and including same in the MPM list.