PURPOSE: To surely prevent mutual collision of X-ray detectors with a simple mechanism in an X-ray diffractor equipped with two goniometers.

CONSTITUTION: The X-ray diffractor has two goniometers 2, 2' with an X-ray source 1 in between. The rotary shaft of an X-ray detector 4 of one goniometer 2 is connected with one end of a wire 6, and the rotary shaft of an X-ray detector 4' of the other goniometer 2' to the other end of the wire 6 to couple both goniometers 2, 2'. The wire 6 is provided with a switch 7 which operates upon application of a predetermined or more tensile force, so that interference is detected by information from the switch 7 before or when the X-ray detectors 4, 4' of both the goniometers 2, 2' interfere.