An inter-prediction method according to the present invention comprises the steps of: deriving a first motion vector of a current block; deriving a first reference block with respect to a current subunit of the current block on the basis of the first motion vector, the current subunit being adjacent to a target boundary of the current block; deriving a second reference block with respect to the current subunit on the basis of a second motion vector of a neighboring block adjacent to the target boundary; and generating prediction samples on the basis of an illumination compensation (IC)-based weighted sum of the first reference block and second reference block. The present invention enables reduction of the amount of data of additional information as well as efficient illumination compensation-based inter-prediction and block boundary error reduction.