1. A motion detection apparatus comprising: a frame memory for frame-delaying a video input signal; a subtracter for calculating a difference between the video input signal and a frame delay signal read out from the frame memory; a comparison portion for comparing an output of the subtracter with an arbitrary threshold value; a first line memory for delaying a signal outputted from the comparison portion; a second line memory for further delaying the signal of the first line memory; and a block discrimination portion for calculating a sum of pixels inside a block constituted by each pixel of a video signal as a center and a plurality of pixels adjacent to the center pixel in both horizontal and vertical directions, for the output from the comparison portion, the output from the first line memory and the output from the second line memory, and comparing the sum with an arbitrary threshold value.