1. In a motion vector detection apparatus for, in order to obtain a motion vector between a reference image and a current original image, matching and searching, with a macroblock (MB) currently processed in the original image, a search region of the reference image which region is set around a position corresponding to the macroblock (MB), a method of determining the search region comprising: determining (a determination step) a search unit with a size and a ratio of height to width such that the search region made up of an aggregation of the search units suitable for the configuration of the search region can be configured; obtaining (a statistics calculation step) a statistics amount of obtained motion vectors in a vector information readout region of the original image set around a position of the MB being processed or in a vector information readout region of the reference image set around a position corresponding to the MB being processed; analyzing (an analysis step) the statistics amount, thereby predicting an appearance tendency of a motion vector; and deciding (a decision step) a combination of search units so as to form an expanded search region expanded in a direction to increase an occurrence probability of a motion vector for the MB being processed based on the analysis.