Bidirectional prediction method and video decoding apparatus

A method of inter-predicting a current block using any one of a plurality of bi-prediction modes is disclosed. The method comprises decoding, from a bitstream, mode information indicating whether a first mode included in the plurality of bi-prediction modes is applied to the current block. When the mode information indicates that the first mode is applied to the current block, the method further comprises: decoding, from the bitstream, first motion information including differential motion vector information and predicted motion vector information for a first motion vector and second motion information not including at least a portion of predicted motion vector information and differential motion vector information for a second motion vector; and deriving the first motion vector based on the first motion information and deriving the second motion vector based on both at least a portion of the first motion information and the second motion information.