A picture coding device using a merge mode, the picture coding device comprising: a merging candidate list constructor (341, 342, 344, 345, 346) structured to construct a merging candidate list including merging candidates; a merging candidate selector structured to select a merging candidate being uni-prediction or bi-prediction from the merging candidate list based on a merge index; and a triangle merging candidate selector structured to select a first triangle merging candidate being uni-prediction from the merging candidate list based on a first triangle merge index and select a second triangle merging candidate being uni-prediction from the merging candidate list based on a second triangle merge index, characterized in that,the first triangle merging candidate of a merge triangular partition 0 is selected with priority on the merging candidate in L0 direction over the merging candidate in L1 direction, the second triangle merging candidate of a merge triangular partition 1is selected with priority on the merging candidate in L1 direction over the merging candidate in L0 direction, the first triangle merging candidate and the second triangle merging candidate are applied to 4x4 sub-blocks with uni-prediction partition 0, uni-predictive partition 1, and bi-prediction partition, the sub-block on an upper side of a diagonal line is assigned to the uni-prediction partition 0, the sub-block on a lower side of the diagonal line is assigned to the uni-prediction partition 1, and the sub-block on the diagonal line is assigned to the bi-prediction partition, and the maximum number of the first triangle merge index is different from the maximum number of the second triangle merge index. a merging candidate list constructor (341, 342, 344, 345, 346) structured to construct a merging candidate list including merging candidates; a merging candidate selector structured to select a merging candidate being uni-prediction or bi-prediction from the merging candidate list based on a merge index; and a triangle merging candidate selector structured to select a first triangle merging candidate being uni-prediction from the merging candidate list based on a first triangle merge index and select a second triangle merging candidate being uni-prediction from the merging candidate list based on a second triangle merge index, characterized in that,the first triangle merging candidate of a merge triangular partition 0 is selected with priority on the merging candidate in L0 direction over the merging candidate in L1 direction, the second triangle merging candidate of a merge triangular partition 1is selected with priority on the merging candidate in L1 direction over the merging candidate in L0 direction, the first triangle merging candidate and the second triangle merging candidate are applied to 4x4 sub-blocks with uni-prediction partition 0, uni-predictive partition 1, and bi-prediction partition, the sub-block on an upper side of a diagonal line is assigned to the uni-prediction partition 0, the sub-block on a lower side of the diagonal line is assigned to the uni-prediction partition 1, and the sub-block on the diagonal line is assigned to the bi-prediction partition, and the maximum number of the first triangle merge index is different from the maximum number of the second triangle merge index.