1. A method of decoding a moving picture, comprising: a step of generating a prediction block of a current prediction unit; and a step of generating a residual block of the current prediction unit, wherein the step of generating a prediction block of the current prediction unit comprises the steps of obtaining a reference picture index and motion vector difference of the current prediction unit from a received bit stream; constructing a motion vector candidate list using available spatial and temporal motion vector candidates; adding zero vector to the motion vector candidate list if a number of the available motion vector candidates is smaller than a predetermined number; determining a motion vector candidate indicated by a motion vector index as a motion vector predictor and restoring a motion vector of the current prediction unit using the motion vector difference and the motion vector predictor; and generating a prediction block of the current prediction unit using the restored motion vector and the reference picture index, wherein the temporal motion vector candidate is a first available motion vector encountered when retrieving two blocks corresponding to the current prediction unit or a motion vector of a predetermined block.