PURPOSE: To project synchrotron radiation light with a good symmetricity to the surface perpendicular to its light axis and unify the intensity distribution by moving independently two horizontal moving plates and two vertical moving plates for a variable slit having an inclination function and inclining it freely to the direction perpendicular to the end surface.

CONSTITUTION: When a first horizontal moving plate 21 is moved with the first and another, horizontal rods 25, 25' driven by a drive mechanism, if the rods are moved to the same direction and the same distance, the moving plate 21 is moved horizontally. If the moving distance is different even if the moving direction is opposite or the same, the end surface of the moving plate 21 inclines slightly against the vertical direction. Similarly, the second horizontal moving plate 22, the first and second vertical moving plates 23, 24 can be moved horizontally and with free inclination of the end surfaces 22a, 22a, 24a using the moving rods 26, 26', 27, 27', 28, 28'. By this, the intensity distribution of the synchrotron radiation light on the base plate can be controlled to be uniform.