Abstract: A motion estimation method using adaptive mode decision is disclosed. The method includes a motion vector difference value calculation step of calculating a motion vector difference value using an input motion vector estimation value x component for a current block and an input x offset corresponding to a current SAD. At the MVD Variable Length Coding (VLC) step, the length of a bit string, which is obtained by performing variable-length coding on an MVDx, is calculated. At a motion vector difference value calculation step, a motion vector difference value is calculated using an input motion vector estimation value y component for a current block and an input y offset corresponding to the current SAD. At an MVD VLC step, the length of a bit string, which is obtained by performing variable-length coding on an MVDy, is calculated. Thereafter, the amount of motion vector coding is produced by adding the MVDx and the MVDy.