A wavelength dispersive X-ray fluorescence spectrometer which comprises: an X-ray source for irradiating a sample with primary X-rays; a spectroscopic device for monochromating fluorescent X-rays emitted from the sample; a detector for receiving the fluorescent X-rays, which have been monochromated by the spectroscopic device, and generating pulses of a pulse height proportional to an energy of the fluorescent X-rays in a number dependent on the intensity of the fluorescent X-rays; a pulse height analyzer for selecting pulses of a pulse height within a predetermined pulse height range from the pulses generated by the detector; a counting unit for determining a counting rate of the pulses selected by the pulse height analyzer; characterized in that the wavelength dispersive X-ray fluorescence spectrometer further comprises: a counting loss correcting unit (11, 12) for correcting the counting rate of the pulses, determined by the counting unit, on the basis of a dead time of the detector with respect to a counting loss of the pulses to be counted; the counting loss correcting unit stores beforehand a correlation between each of a plurality of representative predetermined pulse height ranges and the dead time, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the correlation so stored, or the counting loss correction unit stores beforehand a plurality of pulse height distributions for their respective counting rates, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the pulse height distributions and the counting rates so stored. an X-ray source for irradiating a sample with primary X-rays; a spectroscopic device for monochromating fluorescent X-rays emitted from the sample; a detector for receiving the fluorescent X-rays, which have been monochromated by the spectroscopic device, and generating pulses of a pulse height proportional to an energy of the fluorescent X-rays in a number dependent on the intensity of the fluorescent X-rays; a pulse height analyzer for selecting pulses of a pulse height within a predetermined pulse height range from the pulses generated by the detector; a counting unit for determining a counting rate of the pulses selected by the pulse height analyzer; characterized in that the wavelength dispersive X-ray fluorescence spectrometer further comprises: a counting loss correcting unit (11, 12) for correcting the counting rate of the pulses, determined by the counting unit, on the basis of a dead time of the detector with respect to a counting loss of the pulses to be counted; the counting loss correcting unit stores beforehand a correlation between each of a plurality of representative predetermined pulse height ranges and the dead time, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the correlation so stored, or the counting loss correction unit stores beforehand a plurality of pulse height distributions for their respective counting rates, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the pulse height distributions and the counting rates so stored. a counting loss correcting unit (11, 12) for correcting the counting rate of the pulses, determined by the counting unit, on the basis of a dead time of the detector with respect to a counting loss of the pulses to be counted; the counting loss correcting unit stores beforehand a correlation between each of a plurality of representative predetermined pulse height ranges and the dead time, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the correlation so stored, or the counting loss correction unit stores beforehand a plurality of pulse height distributions for their respective counting rates, and determines the dead time, which corresponds to the predetermined pulse height range during a measurement, on the basis of the pulse height distributions and the counting rates so stored.