An apparatus for transmitting a motion vector together with picture data, comprising: first means adapted to transmit one or two motion vectors corresponding to a prediction mode for a macroblock, if said macroblock is not divided; and second means adapted to transmit one or two first motion vectors corresponding to a prediction mode for a first sub-macroblock and one or two second motion vectors corresponding to a prediction mode for a second sub-macroblock, if said macroblock is divided into said first sub-macroblock and said second sub-macroblock; characterized by: third means adapted to transmit motion vectors which satisfy a condition and discard motion vectors which do not satisfy the condition, if said macroblock is divided into four sub-macroblocks, wherein said condition is that if a motion vector is a forward or backward motion vector of each of one or more secondary sub-macroblocks which are uni-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblock, then such a vector satisfies the condition and optionally if two motion vectors are forward and backward motion vectors of each of one or more secondary sub-macroblocks which are bi-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblocks, then such two motion vectors satisfy the condition unless all of the four sub-macroblocks are bi-directionally predicted, wherein the secondary sub-macroblocks are obtained by dividing each sub-macroblock. first means adapted to transmit one or two motion vectors corresponding to a prediction mode for a macroblock, if said macroblock is not divided; and second means adapted to transmit one or two first motion vectors corresponding to a prediction mode for a first sub-macroblock and one or two second motion vectors corresponding to a prediction mode for a second sub-macroblock, if said macroblock is divided into said first sub-macroblock and said second sub-macroblock; characterized by: third means adapted to transmit motion vectors which satisfy a condition and discard motion vectors which do not satisfy the condition, if said macroblock is divided into four sub-macroblocks, wherein said condition is that if a motion vector is a forward or backward motion vector of each of one or more secondary sub-macroblocks which are uni-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblock, then such a vector satisfies the condition and optionally if two motion vectors are forward and backward motion vectors of each of one or more secondary sub-macroblocks which are bi-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblocks, then such two motion vectors satisfy the condition unless all of the four sub-macroblocks are bi-directionally predicted, wherein the secondary sub-macroblocks are obtained by dividing each sub-macroblock. third means adapted to transmit motion vectors which satisfy a condition and discard motion vectors which do not satisfy the condition, if said macroblock is divided into four sub-macroblocks, wherein said condition is that if a motion vector is a forward or backward motion vector of each of one or more secondary sub-macroblocks which are uni-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblock, then such a vector satisfies the condition and optionally if two motion vectors are forward and backward motion vectors of each of one or more secondary sub-macroblocks which are bi-directionally predicted among secondary sub-macroblocks which include a pixel at a corner of said macroblocks, then such two motion vectors satisfy the condition unless all of the four sub-macroblocks are bi-directionally predicted, wherein the secondary sub-macroblocks are obtained by dividing each sub-macroblock.