An electron microscope is provided which can measure, with high sensitivity and high positional resolution, an amount of deflection of an electron beam occurung when it is transmitted through a sample. The electron microscope (100) is adapted to measure the amount of deflection of the electron beam (EB) when it is transmitted through the sample (S), and has an electron beam source (10) producing the electron beam (EB), an illumination lens system for focusing the electron beam (EB) onto the sample (S), an aperture (30) having an electron beam blocking portion (32) for providing a shield between a central portion (EB1) and an outer peripheral portion (EB2) of the cross section of the beam (EB) impinging on the sample (S), and a segmented detector (20) having a detection surface (22) for detecting the electron beam (EB) transmitted through the sample (S). The detection surface (22) is divided into a plurality of detector segments (D1-D4).
