1. An apparatus for total reflection X-ray fluorescence spectroscopy of irradiating primary X-rays to a measured sample at an angle near a critical total reflection angle, and measuring a characteristic X-ray spectrum emitted from the measured sample by the primary X-rays thereby analyzing an analyzed element on the measured sample, wherein the apparatus comprises an X-ray intensity measuring means for irradiating primary X-rays previously on a standard sample having substantially the same composition as that of a measured sample having a smooth surface at a plurality of irradiation angles near a total reflection angle, means for determining a characteristic X-ray intensity for an analyzed element and a scattered X-ray intensity at a wavelength of the characteristic X-rays for the analyzed element, a function memory means for determining a calibration coefficient indicative of a relation between the characteristic X-ray intensity determined by the X-ray intensity measuring means for the standard sample and a known quantity of the analyzed element on the basis of both of them as a function of the scattered X-ray intensity and storing the function, an X-ray intensity measuring means for measuring a characteristic X-ray spectrum when the primary X-rays are irradiated to the measured sample at an angle smaller than a critical total reflection angle and determining a characteristic X-ray intensity for the analyzed element appearing in the characteristic X-ray spectrum and a scattered X-ray intensity at a wavelength of the characteristic X-rays for the analyzed element, a calibration coefficient calculation means for determining a calibration coefficient by substituting the scattered X-ray intensity determined by the X-ray intensity measuring means for the measured sample as a scattered X-ray intensity of the function stored in the function memory means, and a calculation means for calibrating the characteristic X-ray intensity for the analyzed element determined by the calibration coefficient calculation means and calculating the quantity of the analyzed element.