1. A motion vector decoding LSI, comprising: an assigning unit operable to, when at least one block among a plurality of decoded blocks in the neighborhood of a current block has two motion vectors which refer to reference pictures in the same direction in a display order, assign an identifier to each motion vector for respective one of the plurality of decoded blocks; a generating unit operable to generate a predicted motion vector for a motion vector of the current block based on the motion vectors with same identifier among the motion vectors for the plurality of decoded blocks; and a decoding unit operable to decode a coded motion vector for the current block using the predicted motion vector.