Abstract: A scanning transmission-type electron microscope including an annular-shaped detector disposed concentrically with respect to the optical axis of the microscope behind a specimen along the microscope beam path, and means for amplifying output signals generated by the detector. The detector comprises a scintillation detector and the microscope includes a photoelectron multiplier coupled to the detector and disposed outside the microscope beam. A curved light guide is also coupled to the detector and the photoelectron multiplier and includes a canal which extends through the light guide along the microscope axis for permitting the passage of a central ray cone of the electron beam of the microscope through the light guide.