A measurement method capable of easily measuring the directions of detector segments of a segmented detector relative to a scanning transmission electron microscope (STEM) image is provided. The measurement method is for use in an electron microscope equipped with the segmented detector having a detection surface divided into the detector segments. The measurement method is used to measure the directions of the detector segments relative to the STEM image. The method involves defocusing the STEM image to thereby cause a deviation of the STEM image and measuring the directions of the detector segments relative to the STEM image from the direction of the deviation of the STEM image (step S11).