1. A motion vector decoding apparatus which generates a predicted motion vector for a current block to be decoded and decodes a coded motion vector of the current block using the predicted motion vector, the apparatus comprising: a neighboring block specifying unit operable to specify neighboring blocks which are located around a current block to be decoded and have already been decoded; a differential motion vector decoding unit operable to decode a coded motion vector of the current block so as to generate a differential motion vector; an assigning unit operable to assign, when at least one block among the neighboring blocks has two motion vectors which refer to reference pictures in the same direction in a display order, an identifier to respective motion vector of the neighboring blocks; a predicted motion vector deriving unit operable to derive the predicted motion vector for each motion vector of the current block by using the motion vector having an identifier which is the same as an identifier assigned to the motion vector of the current block, from among motion vectors of the neighboring blocks; and a motion vector obtaining unit operable to obtain the motion vector of the current block by using the predicted motion vector and the differential motion vector, wherein said predicted motion vector deriving unit is operable to: select a motion vector which refers to the same reference picture as referred to by the motion vector of the current block, from among the motion vectors of the neighboring blocks having the same identifier as the identifier assigned to the motion vector of the current block, and derive a median value of the selected motion vectors as the predicted motion vector of the current block when the selected motion vector of the neighboring blocks is plural.