A wavelength dispersive X-ray fluorescence spectrometer of a focusing optical system, the wavelength dispersive X-ray fluorescence spectrometer comprising: an X-ray source configured to irradiate a sample with primary X-rays ; a divergence slit configured to allow secondary X-rays generated from the sample to pass therethrough; a spectroscopic device configured to monochromate and focus the secondary X-rays that have passed through the divergence slit ; and a single one-dimensional detector having a plurality of detection elements arranged linearly and having a receiving surface perpendicular to an optical axis of focused secondary X-rays obtained by the secondary X-rays being focused by the spectroscopic device , wherein the wavelength dispersive X-ray fluorescence spectrometer comprises a detector position change mechanism for setting a position of the one-dimensional detector such that the position of the one-dimensional detector is freely changed to either a parallel position at which an arrangement direction of the detection elements coincides with a spectral angle direction of the spectroscopic device or an intersection position at which the arrangement direction of the detection elements intersects the spectral angle direction of the spectroscopic device , in a state where the one-dimensional detector is set at the parallel position, the receiving surface of the one-dimensional detector is located at a focal point of the focused secondary X-rays , and in a state where the one-dimensional detector is set at the intersection position, a receiving slit having an opening having a longitudinal direction orthogonal to the spectral angle direction of the spectroscopic device is disposed at the focal point of the focused secondary X-rays , and the receiving surface of the one-dimensional detector is located at a traveling direction side of the focused secondary X-rays farther from the spectroscopic device than the receiving slit . an X-ray source configured to irradiate a sample with primary X-rays ; a divergence slit configured to allow secondary X-rays generated from the sample to pass therethrough; a spectroscopic device configured to monochromate and focus the secondary X-rays that have passed through the divergence slit ; and a single one-dimensional detector having a plurality of detection elements arranged linearly and having a receiving surface perpendicular to an optical axis of focused secondary X-rays obtained by the secondary X-rays being focused by the spectroscopic device , wherein the wavelength dispersive X-ray fluorescence spectrometer comprises a detector position change mechanism for setting a position of the one-dimensional detector such that the position of the one-dimensional detector is freely changed to either a parallel position at which an arrangement direction of the detection elements coincides with a spectral angle direction of the spectroscopic device or an intersection position at which the arrangement direction of the detection elements intersects the spectral angle direction of the spectroscopic device , in a state where the one-dimensional detector is set at the parallel position, the receiving surface of the one-dimensional detector is located at a focal point of the focused secondary X-rays , and in a state where the one-dimensional detector is set at the intersection position, a receiving slit having an opening having a longitudinal direction orthogonal to the spectral angle direction of the spectroscopic device is disposed at the focal point of the focused secondary X-rays , and the receiving surface of the one-dimensional detector is located at a traveling direction side of the focused secondary X-rays farther from the spectroscopic device than the receiving slit . <EOS>