1. A moving picture coding device that codes moving pictures using inter-prediction based on inter-prediction information of a merge candidate in units of blocks obtained by partitioning each picture of the moving pictures, comprising: a prediction information coding unit that codes information indicating a designated number of merge candidates; a prediction information deriving unit that derives merge candidates from inter-prediction information of a prediction block neighboring to a coding target prediction block or a prediction block present at the same position as or near the coding target prediction block in a coded picture at a temporally different position from the coding target prediction block; a candidate list constructing unit that constructs a merge candidate list from the derived merge candidates; a candidate supplementing unit that repeatedly adds to the merge candidate list merge candidates of which the prediction mode has the same value, the reference index has the same value, and the motion vector has the same value until the number of merge candidates included in the merge candidate list reaches the designated number of merge candidates when the number of merge candidates included in the merge candidate list is smaller than the designated number of merge candidates; and a motion-compensated prediction unit that selects one merge candidate from the merge candidates included in the merge candidate list and performs inter-prediction on the coding target prediction block using the inter-prediction information of the selected merge candidate.