PURPOSE: To prevent generation of corrosion without attenuation of X-ray strength by forming a beryllium oxide layer on the outer surface of a beryllium window for X-ray take-out provided in a vacuum chamber housing an X-ray source.

CONSTITUTION: A beryllium window 11 of a prescribed thickness is provided on a vacuum chamber 1 housing an X-ray source 2 to take out X-rays 4 through the window 11 to the outside. The outer surface of the window 11 is airtightly held by a stainless steel ring-shaped flange whereon a beryllium oxide layer 12 is formed. The layer 12 is stable against oxygen and moisture in the atmosphere without lowering X-ray transmittance of the window 11 thus to check generation of corrosion. Thereby, an X-ray radiation device can be stably used.