PURPOSE: To obtain a blanking structure which prevents occurrences of contamination at a blanking diaphragm or the surface of a holder by providing two places or more of openings which allow beams to pass through; besides, preparing a cavity part at the lower side of one of the openings.

CONSTITUTION: A blanking diaphragm 8 is equipped with a round opening 10 at a center of the diaphragm as well as a bow-shaped opening 11 at a place that is eccentric from the center and its diaphragm is supported by a holder 9b. In this holder 9b, an opening 14 is provided at the lower part of the opening 10 in the diaphragm 8 and an opening 12 and a cavity 13 are formed at the lower part of the opening 11 in the diaphragm 8. Then, there are more than two places of the openings 10 and 11 in the diaphragm 8 and one of them is formed so that it communicates with the cavity 13 of the holder. Since the effect of charge-up on beam orbits that it caused by occurrence of contamination accompanying the ON-OFF control in the case of writing is minimized exceedingly, pattern lithography with high accuracy is realized for many hours.