1. A motion vector determining apparatus for inter prediction, the motion vector determining apparatus comprising: a reference picture comparing unit for determining whether a reference picture of a candidate block is a same picture as a reference picture of a current block, wherein the candidate block is from among a plurality of candidate blocks referred so as to predict a motion vector of the current block and is spatially adjacent to the current block, and if the reference picture of the candidate block is not the same picture as the reference picture of the current block, determining whether each of the reference picture of the candidate block and the reference picture of the current block is a long-term reference picture; and a motion vector determiner for, if each of the reference picture of the candidate block and the reference picture of the current block is the long-term reference picture, determining a motion vector of the candidate block as a spatial motion vector prediction candidate, without scaling the motion vector of the candidate block, determining motion vector prediction of the current block from among motion vector prediction candidates comprising the spatial motion vector prediction candidate, and generating the motion vector of the current block by using the motion vector prediction.