Abstract: The invention intends to provide a motion vector detecting device capable of increasing the processing speed and simplifying the construction of the device. The motion vector detecting device relating to the invention searches a block most similar to a reduced image of a gazed block from reduced images of the reference region as a first step, and searches a block most similar to the gazed block from a part including the block searched in the first step, of the reference region not reduced, as a second step. And, the motion vector detecting device stores the gazed block and the reference region in the internal memory, and executes the first step and the second step. Further, the device contains an image processing unit that reduces at least one of the gazed block and the reference region into a form that can be used in the first step, and thereafter transfers the reduced one to the internal memory.