A scanning transmission electron microscope (STEM) offering substantially the same ease of operation as that of a scanning electron microscope (SEM) and providing substantially the same degree of resolution as that of a transmission electron microscope (TEM). The STEM of the invention is constituted based on the constitution of the SEM. The STEM comprises: an electron source for generating a primary electron beam; an electron illuminating lens system for converging the primary electron beam from the electron source onto a specimen for illumination; an electron deflecting system for scanning the specimen with the primary electron beam emitted thereto; a scattered electron detector for detecting scattered electrons transmitted through the specimen; a projection lens system for projecting the scattered electrons onto a detection surface of the scattered electron detector; an image displaying device for displaying a scanning transmission electron microscope image of the specimen using a detection signal from the scattered electron detector; and a detection angle changing device for variably establishing a range of scattering angle of the scattered electrons detected by the scattered electron detector. This structure enhances a contrast of a desired portion of the specimen under observation for a scanning transmitted image by selective establishment of detection angle ranges for the scattered electron detector.