A transmission electron microscope (hereinafter, referred to as “TEM”) is a device which applies an electron beam accelerated by a high voltage to an observation object material and focuses the electron beam transmitted through the material into an enlarged image by means of an electromagnetic lens for microstructure imaging. In a state where an imaging lens is focused on the observation object material (specimen), amplitude information on a field formed principally by electrons transmitted through the specimen is observed as image contrast. It is difficult to obtain an image having sufficient contrast from a specimen, such as biological specimen and organic material, that exhibits a small amplitude change. A method which secures a good image contrast by blocking a part of diffracted wave with a knife edge is known as one of methods for obtaining an image of good contrast from such a specimen exhibiting small amplitude change (Patent Literature 1).