PURPOSE: To make the adjustment of a complicated Wien filter unnecessary by reading the data responding to a designated accelera tion voltage and the ion sort from a memory when the acceleration voltage and the ion sort are designated, and controlling the electric field power source and/or the magnetic field power source of the Wien filter depending on this data.

CONSTITUTION: From an ion emitter 1, plural sorts of ions are drawn out responding to the voltage applied to a drawing-out electrode 2, accelerated by an acceleration electrode 3, and the crossover is focused at the center of a Wien filter 5 by a focus lens 4. In the Wien filter 5, only an ion sort responding to the intensity of the electric field and the magnetic field passes straight, and only the selected ion beams are focused slender on a target 8 by an object lens 6. In a memory 17, the data responding to the intensity of the electric field and the magnetic field in the Wien filter responding to the ion sort and the acceleration voltage is stored. When the ion sort is selected by manipulating an ion sort designation knob 18a, a control unit 15 controls an electric field power source 12 and a magnetic field power source 13 depending on the data. Therefore, the adjustment of the Wien filter by a complicated manual handling is not necessary and the handling is made easier.