PURPOSE:To improve the accuracy of potential measurement, by providing a potential barrier to cut off the leakage electrons. CONSTITUTION:An electric field area is arranged to make a barrier against the secondary electrons generated within a mirror body between a throttle 21 and an energy analyzer. A positive potential 24 of 5V is applied to the throttle 21. As a result, an electric field E is produced to make a barrier against the leaked secondary electrons 28, just under the throttle 21, and moreover, a potential sufficient to expel the secondary electrons is given. Therefore, the leaked secondary electrons 28 can never reach to the sample 11, producing no measuring error owing to the leaked secondary electrons. When the device is composed to measure the current flowing in the throttle 21, it may be composed to superpose a positive potential 24 at the input side passage of an ampere meter (or amplifier).
