PURPOSE: To obtain an energy selecting function of a reflected electron which scarcely exerts a bad influence on an irradiated electron ray by a simple structure without generating a retarding voltage in the vicinity of a sample by providing a holding means for inserting and detaching a filter to the reflected electron, in front of the detecting surface of a reflected electron detecting element.

CONSTITUTION: The lower magnetic pole piece 2 of an objective lens is provided on the upper part of a sample room 1, and a reflected electron detecting device is placed between the lower magnetic pole piece 2 and a sample 3. This detecting device consists of a scintillator 6 of a right angle prism type, a light pipe 7 and a photoelectric multiplier 8. Also, this disk-shaped filters 11, 12 held by a filter holding means 8 are placed between the scintillator 6 and the sample 3. According to this constitution, a reflected electron 15 generated by irradiating a sample by an electron ray 14 transmits through the filter 12, is made incident to the lower face of the scintillator 6 and converted to a light beam. The light beam is reflected by the inside surface of the scintillator 6, collected in the direction of the light pipe 7, made incident to the multiplier 8 transduced to an electric signal. Subsequently, the reflected electron of weak energy is cut to detect only the reflected electron of high energy.