1. An apparatus for detecting a motion vector between a current frame and a previous frame of digital video signals, wherein the current frame is divided into a multiplicity of generally large panning blocks, each of the panning blocks having a plurality of subblocks, which comprises: a subblock motion vector detector for detecting a subblock motion vector for each of the subblocks included in a panning block within the current frame; a panning vector detector for detecting a panning vector for the panning block, wherein said panning vector detector includes: means, in response to each of the subblock motion vectors applied thereto from the subblock motion vector detector, for counting the number of the subblock motion vectors with an identical displacement with respect to the panning block so as to determine a maximum counted number of the subblock motion vectors with the identical displacement; means for storing the subblock motion vector at the time of the determined maximum counted number; means for comparing the maximum counted number of the subblock motion vectors with a predetermined threshold number; and means for assigning as the panning vector the subblock motion vector in said storing means when it is determined that the maximum counted number is greater than the predetermined threshold number; a motion vector determination circuit for determining whether the mean absolute value of the difference signals obtained by subtracting the panning block from a motion-compensated previous frame block generated from the previous frame by using the panning vector is greater or smaller than a predetermined reference value to produce a control signal; and means, in response to the control signal, for selecting the subblock motion vector from the subblock motion vector detector or the panning vector from the panning vector detector as an output of the apparatus for determining motion vectors.