Scanning electron microscope

In a scanning electron microscope for displaying a transmitted electron image comprising an electron optical system for focusing and scanning an electron beam generated by an electron gun over a thin film specimen and a means for displaying a scanning image on a cathode-ray tube synchronized with said electron beam scanning by modulating the cathode-ray tube brightness according to the detection signal of the electrons transmitted through the specimen, the improvement comprising a plurality of annular shaped detectors whose common center coincides with the optical axis of said electron optical system for producing a plurality of output signals according to the scattering angle of the elastically scattered electrons transmitted through the specimen and a signal processing means which comprises a comparison circuit for comparing the signal ratio of two output signals of said annular detectors with a constant signal indicative of some component of the specimen and a means for controlling a gate circuit arranged between the cathode-ray tube and said annular detectors according to the output of said comparison circuit.