PURPOSE: To minimize the intensity loss due to the intensity scattering correction by providing a slit of which opening width gradually becomes larger from the center of the scanning in the directions to the both ends, and limiting the scanning direction width of passing synchrotron radiation light.

CONSTITUTION: Between a light source 2 emitting synchrotron radiation light and a scanning type toroidal mirror 3, a slit 1 is provided. The slit 1 shape has a variable vertical (scanning direction of toroidal mirror) opening width in the horizontal direction (radiation light scattering direction) and the opening width increases from the center to both sides. By swinging the radiation light having passed the slit 1 with the toroidal mirror 3, a sample 12 is scanned. At the state where the radiation light having passed the slit 1 is condensed with the toroidal mirror 3, the strength irregularity is already corrected and it is not necessary to pass another toroidal mirror and the like. Thus, the strength loss of radiation light can be minimized.