A method of and apparatus for displaying an image of phase contrast in a scanning transmission electron microscope, in which an electron beam flux transmitted through a specimen is deflected with a high frequency and repeatedly moved on an aperture provided in a region where a transmitted electron beam and a scattered electron beam interfere, and among signal components detected by a detector through the aperture, only a signal synchronous with the high frequency is sampled and detection-rectified, whereby the difference of the intensities of the region where both the electron beams interfere is detected so as to display the image of phase contrast of the specimen.