1. A motion vector decoding method for decoding a coded motion vector of a current block in a moving picture, comprising: specifying a neighboring block which is located in a neighborhood of the current block and is previously decoded; deriving a predictive motion vector of the current block using a motion vector of the neighboring block; and decoding the coded motion vector of the current block using the predictive motion vector; wherein, in case that the neighboring block is decoded using a motion vector of another block, a different motion vector, which is obtained using the motion vector of said another block and which is used in performing a decoding process for the neighboring block, is used as the motion vector of the neighboring block in the deriving.