1. An image still area determination device, comprising: an adjacent pixel value averaging unit for calculating an average value of values of the relevant pixel and pixels adjacent to the pixel in each of two frames when a current frame image and a frame image immediately before it are inputted; a pixel value difference extraction unit for calculating a difference between the average values of values of a pair of pixels in the same position of each of the two frame images; and a still area determination unit for determining a still area of each of the two frame images, using an output of the pixel value difference extraction unit and a predetermined threshold value.