The present invention provides a method for manufacturing a polarizing film, by which, even when a wide raw film is used, it is possible to obtain a polarizing film that achieves excellent optical characteristics as well as uniformity in in-plane optical characteristics. The hand-grip is fashioned and positioned such that it permits operation of the microscope in all directions with only one hand. Next, the method creates differential images between all the elemental images and the respective average images and between the inferior average images and the respective superior average and calculates compressed differential images by compressing the differential images.