An image decoding device comprising: a merge candidate list generation unit that generates a merge candidate list including, as a merge candidate, a spatial merge candidate having motion information on a plurality of blocks neighboring a block subject to prediction and a temporal merge candidate having motion information having a motion vector derived by scaling a motion vector of a block on a decoded image located at the same position as the block subject to prediction; a merge candidate selection unit that selects, as a selected merge candidate that is motion information of the block subject to prediction, a merge candidate from the merge candidate list; a bitstream decoding unit that decodes a bitstream to derive a merge correction flag indicating whether to correct the merge candidate and a motion vector difference that is shared for a motion vector of the selected merge candidate for a first prediction and a motion vector of the selected merge candidate for a second prediction when the merge correction flag indicates that the merge candidate is corrected; and a merge candidate correction unit that derives a corrected merge candidate of bidirectional prediction by adding the motion vector difference to a motion vector of the selected merge candidate for a first prediction and subtracting the motion vector difference from a motion vector of the selected merge candidate for a second prediction, when the merge correction flag indicates that the merge candidate is corrected and a reference picture of the selected merge candidate for a first prediction or a reference picture of the selected merge candidate for a second prediction is a long-term reference picture, the corrected merge candidate being derived from the motion vector of the selected merge candidate for the first prediction and the motion vector of the selected merge candidate for the second prediction that is different from the motion vector of the selected merge candidate for the first prediction. a merge candidate list generation unit that generates a merge candidate list including, as a merge candidate, a spatial merge candidate having motion information on a plurality of blocks neighboring a block subject to prediction and a temporal merge candidate having motion information having a motion vector derived by scaling a motion vector of a block on a decoded image located at the same position as the block subject to prediction; a merge candidate selection unit that selects, as a selected merge candidate that is motion information of the block subject to prediction, a merge candidate from the merge candidate list; a bitstream decoding unit that decodes a bitstream to derive a merge correction flag indicating whether to correct the merge candidate and a motion vector difference that is shared for a motion vector of the selected merge candidate for a first prediction and a motion vector of the selected merge candidate for a second prediction when the merge correction flag indicates that the merge candidate is corrected; and a merge candidate correction unit that derives a corrected merge candidate of bidirectional prediction by adding the motion vector difference to a motion vector of the selected merge candidate for a first prediction and subtracting the motion vector difference from a motion vector of the selected merge candidate for a second prediction, when the merge correction flag indicates that the merge candidate is corrected and a reference picture of the selected merge candidate for a first prediction or a reference picture of the selected merge candidate for a second prediction is a long-term reference picture, the corrected merge candidate being derived from the motion vector of the selected merge candidate for the first prediction and the motion vector of the selected merge candidate for the second prediction that is different from the motion vector of the selected merge candidate for the first prediction.