PURPOSE: To aim at automation of up to the attraction of a sample on a base plate with a simple device, by impressing the voltage that attracts the sample to an interval between the base plate and a sample electrode from a DC high voltage power source and, when the charging voltage exceeds the specified value, making it so as to ascertain the conduction between the sample and the sample electrode.

CONSTITUTION: When a sample electrode 3 is made to come into contact with a sample 2 and an on-switch 15 is closed, a self-holding relaying relay 11 is set in motion by each conductive passage of an off-switch 16 and normally closed contacts 14b and 12b, forming a self- holding circuit by means of a closed passage of a normally opened contact 11a1, while reference voltage to be outputted out of a reference voltage generator 8 by a closed passage of a normally opened contact 11a2 is inputted into a DC voltage power source 4. Next, the power source 4 outputs such high voltage that attracts the sample 2 onto a base plate 1 by input of the reference voltage, impressing it on an interval between the base plate 1 and the sample electrode 3. Hereat, output voltage V of the power source 4, immediately after impressing, is almost added to the interval between the sample 2 and the sample electrode 3, inducing a dielectric breakdown there, and since the interval between the sample 2 and the sample electrode 3 is conducted, the sample 2 is automatically attracted on the base plate 1 without using another power source and a dielectric breakdown device.