1. A motion compensation method for coding or decoding an image signal, the motion compensation method comprising: a selection step of selecting one of methods for generating a motion vector of a block in a current macroblock to be coded or decoded, depending on a motion vector of a block located in a corner of a coded or decoded macroblock among a group of blocks that compose the coded or decoded macroblock corresponding to the current macroblock; and a motion compensation step of generating a predictive image of the block in the current macroblock based on the motion vector generated by the selected method.