To provide a beam shaping aperture which has no round corner sections.

A rectangular upper carved hole 2 is formed into a single discoid member (made of tantalum or molybdenum), from the upper surface of the member to the central part of the member in the thickness direction. In addition, a rectangular lower carved hole 3 is formed into the member, extending from the lower surface of the member to the central part of the member in the thickness direction. These holes 2 and 3 overlap each other and form an opening at the central part. Since the holes 2 and 3 intersect each other at right angles, the opening also becomes rectangular (in many cases, square) in shape. Although the holes 2 and 3 have round corner sections formed at the time of carving the holes 2 and 3, the rectangular opening has no round corner section.