An X-ray analysis instrument, in particular, an X-ray diffractometer (21), has an X-ray source (22; SC) that emits an X-ray beam (23), an X-ray optics (24), in particular a multi-layer X-ray mirror, and a collimator mechanism (BM), wherein the collimator mechanism (BM) forms an aperture window (2, 2′) with an aperture opening (3, 3′) through which at least part (26) of the X-ray beam (23) passes. The collimator mechanism (BM) comprises means for gradual movement of the aperture window (2, 2′) in at least one direction (A/B, x,y) transversely to the X-ray beam (23), the aperture opening (3, 3′) is at least as large as the cross-section (32) of the X-ray beam (23) at the location of the aperture window (2, 2′), and the path of movement (VWx, VWy) of the aperture window (2, 2′), which is accessible by the collimator mechanism (BM), in the at least one direction (A/B, x, y) is at least twice as large as the extension (RSx, RSy) of the X-ray beam (23) at the location of the aperture window (2, 2′) in this direction (A/B, x, y). The X-ray analysis instrument offers a wider scope of beam conditioning possibilities.