PURPOSE: To facilitate observation of the surface image of a sample by maintaining the electric potential of the surface of the sample constant by installing an electric- discharge device inside the sample chamber of a usual scanning electron microscope, and instantaneously making a conductive matter in contact with an insulating material provided on the surface of the sample, which is charged by electric radiation, so as to discharge electric charges developed on the surface of the sample.

CONSTITUTION: When a current (I) is fed to an electromagnetic coil 25, a core 24 is pulled in toward the center of the core 24, and accordingly, a supporting pin 21 and a contact 7 are extended. When the current (I) is not fed to the coil 25, the core 24 and the contact 7 contract into their original states due to a spring 26. Therefore, the slant and the stroke of the contact 7 can be appropriately set according to the conditions of a sample 5 and a sample stand 4. The contact 7 is made of a conductive matter which doesn't deteriorate the surface of the sample 5 when it touches the surface of the sample 5, such as a soft conductive rubber. A voluntary electric potential can be applied to the contact 7 from a lead wire 22, and the electric potential of the surface of the sample 5 can be voluntarily set when the contact 7 touches the surface of the sample 5.