Motion detecting apparatus, motion detecting method, and storage medium storing motion detecting program for avoiding incorrect detection

To provide a motion detecting apparatus that judges whether each macro block shows a part of an object in motion using motion vectors calculated by a general-purpose MPEG video encoder during motion compensation. The motion detecting apparatus compares a motion vector of a present macro block with motion vectors of macro blocks surrounding the present macro block. If the motion vector of the present macro block and the motion vectors of the surrounding macro blocks are not random in direction and magnitude, the motion detecting apparatus judges that the present macro block shows a part of an object in motion. Otherwise, the motion detecting apparatus judges that the present macro block does not show a part of an object in motion.