An image decoding method performed by a decoding apparatus according to the present invention is characterised by comprising the steps of: deriving a reference picture list 0 (L0) and a reference picture list 1 (L1); deriving two motion vectors (MV) for a current block, wherein the two MVs include MVL0 for the L0 and MVL1 for the L1; determining whether to apply BIO prediction that derives motion vectors for each sample in the current block based on the MVL0 and the MVL1; deriving motion vectors for each sample in the current block based on the MVL0 and the MVL1 if it is determined to apply the BIO prediction; and deriving a prediction sample based on the motion vectors for each sample.