Abstract: A method and an apparatus for detecting the number of persons in which the differential pictures are converted into binary signals being affected neither by the color of the hair of the persons to be detected nor by the change in the intensity of illumination even when the contrast is small over the background floor. The shape of the picture is corrected, and the area of the picture becomes nearly uniform irrespective of the positions of the persons in the visual field of the TV camera. Moreover, a correlation value relative to the pattern of a predetermined size and a center of gravity of the picture are found while compressing the number of pixels, making it possible to detect the number of persons within a very short period of time maintaining high precision.