PURPOSE: To obtain high X-ray output strength and average X-ray strength at an X-ray receiving part by reflecting X-rays irradiated as divergent light from a spot at a reflecting surface of a revaluing reflecting mirror of paraboloid.

CONSTITUTION: When an electron beam 12 is projected on a metal surface 14, an X-ray 16 is emitted therefrom. At this time divergent light 161, 162... is reflected on the reflecting surface 10a of a reflecting mirror 10 to make parallel light, and converged as effective X-rays to reach a light receiving part. In other words ineffective divergent light is used effectively as it remains large strength by the reflection of paraboloid surface and so whole X-ray output strength can be improved. The film thickness of a large (small) part of incidence angle is made thin (thick) to obtain same reflection factor over the whole surface of the reflecting surface 10a. Therefore, X-ray strength distribution can be averaged at the light receiving part.