A scanning transmission electron microscope that scans a specimen with an electron probe to acquire an image, the scanning transmission electron microscope comprising: an optical system which includes a condenser lens and an objective lens; an imaging device which is arranged on a back focal plane or a plane conjugate to the back focal plane of the objective lens and which is capable of photographing a Ronchigram; and a control unit which performs adjustment of the optical system, the control unit performing processing for: acquiring an image of a change in a Ronchigram that is an image of a Ronchigram having been photographed by the imaging device which is maintained in an exposed state while changing the relative positional relationship between the specimen and the electron probe, or an image obtained by integrating or averaging a plurality of images of a Ronchigram having been acquired under different conditions with respect to the relative positional relationship between the specimen and the electron probe; and determining a center of a Ronchigram based on the image of a change in a Ronchigram, the relative positional relationship between the specimen and the electron probe being a relative positional relationship between the specimen and the electron probe in a direction along an optical axis of the optical system. an optical system which includes a condenser lens and an objective lens; an imaging device which is arranged on a back focal plane or a plane conjugate to the back focal plane of the objective lens and which is capable of photographing a Ronchigram; and a control unit which performs adjustment of the optical system, the control unit performing processing for: acquiring an image of a change in a Ronchigram that is an image of a Ronchigram having been photographed by the imaging device which is maintained in an exposed state while changing the relative positional relationship between the specimen and the electron probe, or an image obtained by integrating or averaging a plurality of images of a Ronchigram having been acquired under different conditions with respect to the relative positional relationship between the specimen and the electron probe; and determining a center of a Ronchigram based on the image of a change in a Ronchigram, the relative positional relationship between the specimen and the electron probe being a relative positional relationship between the specimen and the electron probe in a direction along an optical axis of the optical system. acquiring an image of a change in a Ronchigram that is an image of a Ronchigram having been photographed by the imaging device which is maintained in an exposed state while changing the relative positional relationship between the specimen and the electron probe, or an image obtained by integrating or averaging a plurality of images of a Ronchigram having been acquired under different conditions with respect to the relative positional relationship between the specimen and the electron probe; and determining a center of a Ronchigram based on the image of a change in a Ronchigram, the relative positional relationship between the specimen and the electron probe being a relative positional relationship between the specimen and the electron probe in a direction along an optical axis of the optical system.