PURPOSE: To constitute a charged-particle electrostatic lens with small aberration and high accuracy by forming several lens electrodes located at given intervals along the axial direction on the inner surface of a cylindrical body made of an insulating material such as a ceramic member.

CONSTITUTION: A hot-cathode-type ion gun 1 or the like is constituted by installing a filament 8 and a grid 10 which ionized thermions by accelerating them to collide them with a gas. It is constituted so that an ion beam is converged by being introduced to a charged-particle electrostatic lens 12. The electrostatic lens 12 is formed by applying a conductive substance to the inner surface of a cylinder 20 made of a ceramic member and installing several lens electrodes 24aW24c at given intervals along the axial direction. The lens electrodes 24aW 24c are attached with screws 22. As a result, the electrostatic lens 12 can be assembled with high accuracy without any necessity of axis adjustment, thereby enabling the lens 12 to be made compact.