Patent Number: 
Section: claims

1. An X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex,the four blades having such a structure that the blades are fitted in one another in the form of parallel crosses at portions corresponding to four-corner edges of the pyramid, wherein one of the blades is configured to move from a first position parallel to a second position. 2. An X-ray diaphragm according to claim 1, wherein each of the blades has a plurality of cross beams, the cross beams of the blades being formed such that the adjacent cross beams are fitted in each other. 3. An X-ray diaphragm according to claim 1, wherein the distance between the mutually opposed blades is variable. 4. An X-ray diaphragm according to claim 1, wherein the diaphragm is configured to rotate. 5. An X-ray diaphragm according to claim 1, wherein the diaphragm is configured to rotate in a plane parallel to an axis of an X-ray tube. 6. An X-ray irradiator comprising:an X-ray tube;an X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex; anda collimator for collimating the X-ray beam formed by the X-ray diaphragm,the four blades having such a structure that the blades are fitted in one another in the form of parallel crosses at portions corresponding to four-corner edges of the pyramid, wherein one of the blades is configured to move from a first position parallel to a second position. 7. An X-ray irradiator according to claim 6, wherein each of the blades has a plurality of cross beams, the cross beams of the blades being formed such that the adjacent cross beams are fitted in each other. 8. An X-ray irradiator according to claim 6, wherein the distance between the mutually opposed blades is variable. 9. An X-ray irradiator according to claim 8, wherein the X-ray diaphragm is interlocked with the collimator. 10. An X-ray irradiator according to claim 6, wherein the X-ray diaphragm and the collimator are rotatable in a plane parallel to an axis of the X-ray tube. 11. An X-ray apparatus comprising:an X-ray tube;an X-ray diaphragm having four blades which are arranged in a surrounding relation to four sides so as to form a pyramidal X-ray beam with an X-ray focus as a vertex, wherein a first one of the blades is configured to fit with a second one of the blades, wherein the first one of the blades is conflaured to form a plurality of parallel crosses within the second one of the blades, wherein the parallel crosses are formed at an edge of a pyramid formed by the blades, and wherein the first one of the blades is configured to move from a first position parallel to a second position; anda collimator for collimating the X-ray beam formed by the X-ray diaphragm and directing the collimated beam to an object to be radiographed.