1. A moving picture decoding method for decoding a current block to be decoded included in a current picture to be decoded by inter predictive decoding using a motion vector, the moving picture decoding method comprising: decoding a first flag indicating whether or not temporal motion vector prediction using a temporal motion vector predictor which is a motion vector of a block included in a decoded picture different from the current picture is used; assigning one or more reference picture indexes to a reference picture list; when the first flag indicates that the temporal motion vector prediction is used, decoding a collocated reference picture index for specifying the decoded picture among a plurality of pictures indicated by the one or more reference picture indexes, deriving a plurality of first motion vector predictor candidates including (i) a spatial motion vector predictor which is a motion vector of a block adjacent to the current block in the current picture and (ii) the temporal motion vector predictor, the temporal motion vector predictor being calculated based on a motion vector of the coded picture which is specified by the collocated reference picture index, and decoding a motion vector used for performing inter predictive decoding on the current block using one of the first motion vector predictor candidates; and when the first flag indicates that the temporal motion vector prediction is not used, deriving a plurality of second motion vector predictor candidates that do not include the temporal motion vector predictor, the second motion vector candidates including (i) the spatial motion vector predictor and (ii) a replacement vector, as a replacement for the temporal motion vector predictor, which has a value of zero, and decoding a motion vector used for performing inter predictive decoding on the current block, using one of the second motion vector predictor candidates, wherein when the first flag indicates that the temporal motion vector prediction is not used, the collocated reference picture index is not decoded.