1. A motion vector coding method for generating a motion vector for a current block to be coded and a predicted vector for the motion vector and coding a difference between the motion vector and the predicted vector, the motion vector coding method comprising: an assigning step for, when at least one block among a plurality of coded blocks in the neighborhood of the current block has two motion vectors which refer to reference pictures in the same direction in a display order, assigning IDs to two motion vectors for respective one of the plurality of coded blocks; and a generating step for generating the predicted vector for each of the motion vectors for the current block based on the motion vectors with the same ID among the motion vectors for the plurality of coded blocks.