Abstract: In an X-ray analysis apparatus, there is provided between a test specimen (5) or an analyzing crystal and a detector (9) a stray radiation slit (15) that can be adjusted in dependence on the goniometer angle. By an optimum adjustment of this slit in correspondence with the variation in the goniometer angle it can be achieved that the detector will always see the same portion of the surface of the test sample or analyzing crystal. Especially, the adjustment of the slit is coupled to the adjustment of an automatic divergence slit (11) so that the portion of the surface which is irradiated, remains unaltered. Especially for small goniometer angles, that is to say for the analysis of a substance in which there is a large distance between crystal planes, a considerably improved signal-to-noise ratio in the measurement signal is thus obtained.