An mean (average value) filter apparatus includes first accumulation means (1) for accumulating a predetermined number of pixels located in the vicinity of each pixel in a first dimensional direction for the pixel data arrangement constituting a second dimensional image, thereby generating first accumulation pixel data of each of the pixels, second accumulation means (2) for accumulating the aforementioned first accumulation pixel data for a predetermined number of pixels located in the vicinity of each pixel in the second dimensional direction, thereby generating second accumulation pixel data of each of the pixels, and division means (45) for dividing the second accumulation pixel data by the number of pixels accumulated in the first dimensional direction and the second dimensional direction.