An intra prediction method includes the steps of: acquiring intra prediction mode information from a bitstream; deriving neighboring samples of a current block; determining an intra prediction mode for the current block on the basis of the intra prediction mode information; deriving a prediction sample of the current block on the basis of the intra prediction mode and the neighboring samples; determining filtering reference samples for the prediction sample on the basis of the intra prediction mode; and deriving a filtered prediction sample by applying filtering to the prediction sample on the basis of the filtering reference samples. According to the present invention, a prediction sample can be adaptively filtered according to the intra prediction mode, and intra prediction performance can be improved.