PURPOSE: To introduce secondary electrons generated from an electron shower to a wafer effectively without separation from the ion beam by furnishing an electroconductive cylinder surrounding the irradiated ion beam and having a section with specified dimension, and by installing electron shower within the cylinder.

CONSTITUTION: An electroconductive cylinder 2 surrounding the ion beam 1 to be irradiated to a wafer 7 and having a section a little greater than the beam 1 is arranged close to the surface of the wafer 7. This cylinder is equipped with an electron shower formed from a filament 3, a grid 4, a target 11, and the secondary electrons generated by the electron shower is introduced effectively to the wafer 7 without separation from the beam 1. This enables suppression of positive and negative charging on the wafer to prevent its insulation film from breakage.