A scanning transmission electron microscope is provided including an electron beam source (1), convergent lenses (3), scan coils (10), a dark field image detector (16), a bright field image detector (17), an A/D converter (21), and an information processing device (24). In the scanning transmission electron microscope, a spherical aberration corrector (7) and deflection coils (9a, 9b) are disposed before a pre-magnetic field of objective lens (11). Fourier transform images are produced from scanning transmission images obtained by the dark field image detector (16) or the bright field image detector (17) to evaluate deviation in an aberration correction state due to an image shift caused by the deflection coils (9a, 9b) at a deflection ratio, so a suitable deflection ratio is fed back. As a result, an electron optics of the scanning transmission electron microscope including the corrector can be easily adjusted.