A video decoding method using an inter-prediction is disclosed. The method includes at least: determining a motion vector of a current block to be decoded in a current picture; predicting pixels in current block using the motion vector of the current block; extracting quantized transform coefficients by decoding a bitstream; reconstructing residual signals by inversely quantizing and then inversely transform the quantized transform coefficients; and adding the predicted pixels and the reconstructed residual signals which correspond to the predicted pixels, wherein the determination of the motion vector of the current block comprises: obtaining a flag by decoding a bitstream, the flag indicating one among a plurality of modes for determining the motion vector of the current block.