PURPOSE: To efficiently perform the positioning work of a sample without damaging the surface of the sample by transferring the sample so that the detected output of the fluorescent X-rays emitted from the sample is made maximum.
CONSTITUTION: The sorted peak value of a pulse height analyzer 8 is set to the energy value of characteristic X-rays of the main element of a sample. The initial position of an X-ray detector 6 is made arbitrary but it is convenient that the position on a goniometer G is set to the direction dislocated from the direction of the diffracted X-rays predicated for the sample. When the sample is measured while lowering this sample to the position C from the posi tion A, a counting curve is obtained. The sample can be automatically set to the right position when the sample is fixed to the position equivalent to the peak vertex of this counting curve.