PURPOSE: To prevent the electrostatic breakdown of an element by arranging magnets with respect to an opposite polarity particle generating section so that charged particles with an opposite polarity are faced to the magnetic lines of force existing region including the magnetic flux density minimum region of magnets.

CONSTITUTION: Magnets 3 are arranged so that the magnetic flux density on the axis of a charged particle beam 1 is made minimum and the magnetic flux density is increased apart from the axis. For the layout, two magnets may be arranged so that their N and S poles are faced to each other. Or the magnets 3 are arranged with respect to an opposite polarity particle generating section 2 so that opposite polarity particles pass the magnetic flux density minimum region of the magnets and the potential distribution that almost all particles are concentrated in the region is generated then the particles are fed to a wafer 10. When they are thus arranged and the strength of the magnetic field is adjusted, the distribution of the charged particle beam 1 can be matched with the distribution of opposite polarity particles. The potential of the charged particle beam 2 can be set near the earth potential on the whole wafer.