An image decoding method of decoding a current picture per block with bi-prediction using both of (i) a first reference picture list including a first current reference picture for a current block, the first current reference picture being referred to by a first current motion vector, and (ii) a second reference picture list including a second current reference picture for the current block, the second current reference picture being referred to by a second current motion vector, said method comprising: judging whether or not the second current reference picture for the current block is identical to a second adjacent reference picture for an adjacent block, said adjacent block being adjacent to the current block and decoded with bi-prediction, the second adjacent reference picture being (i) included in a second adjacent reference picture list and (ii) referred to by a second adjacent motion vector; when the second current reference picture is judged to be identical to the second adjacent reference picture, adding the second adjacent motion vector to a candidate list for the second current motion vector; judging whether or not the second current reference picture is identical to a first adjacent reference picture for the adjacent block, the first adjacent reference picture being (i) included in a first adjacent reference picture list and (ii) referred to by the first adjacent motion vector; when the second current reference picture is judged to be identical to the first adjacent reference picture, adding the first adjacent motion vector to the candidate list for the second current motion vector; selecting (S606, S611) a predicted motion vector to be used for decoding the second current motion vector from the candidate list for the second current motion vector; and decoding (S606, S611) the second current motion vector using the selected predicted motion vector, wherein the second judging step is performed when the second current reference picture is judged to not be identical to the second adjacent reference picture. judging whether or not the second current reference picture for the current block is identical to a second adjacent reference picture for an adjacent block, said adjacent block being adjacent to the current block and decoded with bi-prediction, the second adjacent reference picture being (i) included in a second adjacent reference picture list and (ii) referred to by a second adjacent motion vector; when the second current reference picture is judged to be identical to the second adjacent reference picture, adding the second adjacent motion vector to a candidate list for the second current motion vector; judging whether or not the second current reference picture is identical to a first adjacent reference picture for the adjacent block, the first adjacent reference picture being (i) included in a first adjacent reference picture list and (ii) referred to by the first adjacent motion vector; when the second current reference picture is judged to be identical to the first adjacent reference picture, adding the first adjacent motion vector to the candidate list for the second current motion vector; selecting (S606, S611) a predicted motion vector to be used for decoding the second current motion vector from the candidate list for the second current motion vector; and decoding (S606, S611) the second current motion vector using the selected predicted motion vector, wherein the second judging step is performed when the second current reference picture is judged to not be identical to the second adjacent reference picture.