<p>To reduce beam drift in which the orbit of a charged particle beam is deflected by potential gradient produced when the potential of a sample surface is made non-uniform within a charged particle beam irradiation region plane by charging produced when an insulation sample is observed with a charged particle beam. The energy of a charged particle beam applied to a sample is so set that the production efficiency of a secondary electron produced from the sample is at least one. The structure of the device is such that flat electrode (26) that is able to apply a voltage independently and is provided with a hole for permitting the passage of a primary charged particle beam therethrough is disposed facing the sample, a voltage can be applied independently to a sample-mounting sample table (12), and the surface facing the sample is flat and free from unevenness. The diameter D of the hole provided in the flat electrode (26) and the distance L between the flat electrode (26) and the sample are set so as to satisfy the relation D/L=1.5.</p>
