1. A motion estimation method using multiple reference frames, comprising the operations of: analyzing a plurality of reference indexes of a current block, the plurality of reference indexes indicating reference frames of respective ones of a plurality of neighboring blocks that have already been coded; selecting, when all of the neighboring blocks have a same reference value, a single reference frame indicated by one of the plurality of reference indexes of the plurality of neighboring blocks from among the multiple reference frames and performing motion estimation on the current block using the single reference frame, when all of the plurality of neighboring blocks have a same reference index; and performing motion estimation on the current block using all of the multiple reference frames when all of the plurality of neighboring blocks do not have the same reference index.