The picture coding apparatus (300) includes a motion vector estimation unit (302) that select one of methods for deriving a motion vector of a block to be motion-compensated, depending on a motion vector of a block located in a corner of a decoded macroblock among a group of blocks that compose the decoded macroblock corresponding to the current macroblock to be coded and determines the motion vector derived by the selected method for derivation to be a candidate of the motion vector of the current macroblock to be coded and a motion compensation unit (303) that generates a predictive image of the block to be motion-compensated based on the estimated motion vector.