A method and device for observing a specimen in which an electron beam is irradiated and scanned from an oblique direction, onto a surface of a calibration substrate on which a pattern with a known shape is formed, and an SEM image of the surface of the calibration substrate is obtained. An angle in an oblique direction of the electron beam irradiated is obtained and is adjusted to a desired angle. The electron beam is irradiated from the adjusted desired angle in the oblique direction, onto a specimen substrate on which a pattern is formed, and an SEM image of the specimen substrate is obtained. The SEM image of the specimen substrate is processed by use of the information of the desired angle, and a 3D image of the pattern on the specimen substrate or a shape of a cross section of the pattern is obtained.