Disclosed are an inter-prediction method and an image decoding apparatus using the same. According to an embodiment of the present invention, there is provided an inter-prediction method including extracting a merge candidate flag and offset information from a bitstream, selecting a merge candidate corresponding to the extracted merge candidate flag from a merge candidate list including neighboring blocks of a current block as merge candidates, deciding a motion vector of the current block by applying the offset information to a motion vector of the selected merge candidate, and generating, as a prediction block of the current block, a block indicated by the motion vector of the current block in a reference picture referenced by the selected merge candidate.