the same potential and given opposite voltage characteristics instead of the columnar quadrupole lens lenses obtained by dividing a generally used circular plate may be used in an electrostatic deflector as shown in fig3 b in this case the lens can be downsized as shown in fig2 the orbit of a primary beam b 1 having passed through the primary optical system 25 is deflected by the deflecting operation of the wien filter 29 assume that the magnetic field and electric field cross at a right angle and e b and v represent the electric field magnetic field and charged particle speed respectively in this case the wien filter 29 allows only charged particles that satisfy the wien condition of e vb to travel straight and deflects the remaining charged particles the function of the wien filter will be explained as shown in fig5 a 5 b and 5 c a force fb by the magnetic field and a force fe by the electric field are generated for the primary beam b 1 to deflect its beam orbit as for a secondary beam b 2 the forces fb and fe act in opposite directions and cancel each other and thus the secondary beam b 2 travels straight the lens voltage of the primary optical system 25 is set in advance so as to form a primary beam into an image at the aperture portion of.