A method for decoding a video performed by a decoding device according to the present disclosure, comprises: a step for deriving a prediction mode of a neighboring block of a current block; a step for deriving an intra prediction mode candidate for configuring an MPM list on the basis of the derived prediction mode of the neighboring block; a step for configuring the MPM list on the basis of the derived intra prediction mode candidate; a step for determining an intra prediction mode for the current block on the basis of the configured MPM list; a step for deriving prediction samples for the current block on the basis of the determined intra prediction mode for the current block; and a step for generating a reconstructed picture on the basis of the prediction samples.