1. A motion vector detector for detecting a motion vector of a reference pixel in a current input frame with the block matching technique, the detector comprising: a vector calculating means for sequentially calculating a sum of absolute values of differences in pixel between a reference block taking as its origin a reference pixel extracted from a current frame and a search block moving within or along the circumference of a search range extracted from a reference frame, which is one frame after the current frame, to determine the vector of a motion between a pixel position within the search block in which the difference absolute-value sum is smallest and the position of the reference pixel; and a vector correcting means for correcting the quantity of the motion vector determined by the vector calculating means so that the vector quantity falls within the search range in case that the pixel position for the smallest difference absolute-value sum exists outside the search range.