Disclosed herein are a decoding method and apparatus and an encoding method and apparatus that perform inter-prediction using a motion vector predictor. For a candidate block in a col picture, a scaled motion vector is generated based on a motion vector of the candidate block. When the scaled motion vector indicates a target block, a motion vector predictor of the target block is generated based on the motion vector of the candidate block. The motion vector predictor is used to derive the motion vector of the target block in a specific inter-prediction mode such as a merge mode and an AMVP mode.