Apparatus for measuring specimen potential in electron microscope

An apparatus for measuring the specimen potential in an electron microscope includes a first grid arranged to enclose a specimen which is to be irradiated with a primary charged particle beam emitted from the electron source of the electron microscope and to which is supplied a voltage sufficient to attract the secondary electrons emitted from the specimen. A second grid supplied with a voltage sufficient to analyze the energy of the secondary electrons which have passed through the first grid is disposed outside the first grid, and a secondary electron detecting arrangement for detecting the secondary electrons which have passed through the second grid is disposed adjacent the second grid. A current detecting arrangement partly for impressing the voltage upon the first grid and partly for detecting the current flowing through the first grid is provided along with a dividing and amplifying arrangement for dividing the output of the secondary electron detecting arrangement by the output of the current detecting arrangement, whereby the potential at said specimen of the electron microscope is measured with increased sensitivity.