A bi-prediction decoding method includes determining whether or not a current block to be decoded is a bi-prediction coding mode by analyzing the coded data; recovering a decoding target motion vector by decoding the coded data in a case where it is determined that the current block is the bi-prediction coding mode; calculating the recovered decoding target motion vector, and a non-decoding target motion vector corresponding to a second reference picture based on a temporal distance between a current picture to which the current block belongs and a first decoding reference picture corresponding to the decoding target motion vector and a temporal distance between the current picture and a second decoding reference picture; and recovering the current block based on a generated prediction block by generating the prediction block for the current block based on the recovered decoding target motion vector and the calculated non-decoding target motion vector.