PURPOSE: To allow a series of settings of a sample horizontal goniometer with a setting jig attached.

CONSTITUTION: With a reference surface of a setting jig 22 attached to a sample axis 16 horizontal, an X-ray optical system is tilted by 30° from a horizontal plane. At this time, a divergence slit 3, the center line 6 of goniometer rotation and a light receiving slit 9 are on a line. X-rays pass through a through hole 24 of the setting jig 22. An X-ray tube 2 is moved in a direction of an arrow 18 in this state to search for a position of an X-ray detector 8 where detection intensity is maximum. Then the X-ray optical system is set horizontal, and the setting jig 22 is rotated around the center line 6 of goniometer rotation within a very small angle range. Intensity of the X-rays which have passed by reference surfaces 26, 28 of the setting jig 22 is measured, and the sample axis 16 is halted at a position where the detection intensity is maximum.