PURPOSE: To prevent corrosion without a metallic window's contact to the atmosphere, to enable light exposure in the atmosphere and to intend improvement of efficiency of exposure work by forming a cavity outside the metallic window to filled by inert gas.

CONSTITUTION: A metallic window 44, a beryllium window, for instance, is arranged at a beam bringing-out line of an SOR beam (synchrotron orbital radiation beam) device, in order to vacuum-seal the line and bring out the SOR beam, and also a cavity 74 is arranged outside the window 44, inside which an inert gas is filled out to shut off an outer side surface of the window 44 from the atmosphere. Moreover, an X-ray masking membrane window 76 is made of materials to be used for X-ray masking base plate and is arranged at a part of the cavity 74 to project the SOR beam passing through the window 76, to the atmosphere. The SOR beam is projected out to the atmosphere from the window 44 through the cavity 74 and the window 76, and by forming the cavity 74 outside the window 44 to be filled by inert gas, the window 44 does not contact to the atmosphere, corrosion is thus prevented and structural strength is kept long time. Accordingly, light exposure can be well conducted in the atmosphere and efficiency of exposure work is much improved.