The motion vector calculation method for improving the compression rate includes a selection step of selecting one reference motion vector of a reference block, and a calculation of calculating a motion vector of a block to be processed using one reference motion vector selected in the selection step. Step is included, and in the selection step, when the reference block has two reference motion vectors (S121), two references are made based on whether the reference block is in front of or behind the processing target block in display time order. One reference motion vector is selected from the motion vector (S123, S124), and when the reference block has only one reference motion vector (S125, S127), the one reference motion vector is selected (S126, S128). .
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