1. A method for encoding motion vectors comprising: (a) predicting a motion vector of a type identical to that of a motion vector of a present block and obtaining a predictive motion vector with respect to neighbor blocks having motion vectors of a type different from that of the present block among a plurality of neighbor blocks adjacent to the present block; (b) calculating a representative value of the motion vector of a type identical to that of the present block from the motion vectors of the neighbor blocks and the predictive motion vector; (c) calculating a difference value between the calculated representative value and the motion vector of the present block; and (d) encoding the calculated difference value.