An in-lens type objective lens is separated into two parts along the plane perpendicular to the direction of electron or ion orbit, so that a target sample can placed between the upper part and the lower part of the lens. Coils for the two parts are serially connected so as to work as one coil. Each of the upper and lower parts of the lens is provided with a lens positioning device. If the in-lens type objective lens is of a three-piece electrostatic type, a structure is provided which enables a target sample to be placed between a first and second electrode group and the third electrode.