To extract only a moving object except for the area of the moving object by providing a binarizing means discriminating into the area of the moving object and the area except for it by binarization by comparing each pixel value of an AC component image with a threshold value.

An AC component image preparing part 104 devides a background difference image S103 into small areas, orthogonally transforms each small area to extract the featured value of an AC component and prepares an image S104 consisting of a pixel value according to the size to output to a binarizing device 105. The device 105 binarizes by the area of the moving object and the area except for it with the threshold vale from the images S104 and outputs a binarized image S105 to a correction filter 106. Next, a number is assigned to each individual moving object from among binary image S106 outputted from a correction filter 107 to extract the individual moving object.