An X-ray fluorescence spectrometer configured to irradiate, with primary X-rays, a sample having either a) a single-layer thin film formed without a substrate, or b) a multi-layer thin film formed without a substrate, or c) a single-layer thin film formed on a substrate, or d) a multi-layer thin film formed on a substrate, and configured to obtain quantitative values of a composition and/or a thickness of the thin film by a fundamental parameter method on the basis of measured intensities of generated secondary X-rays, the spectrometer comprising: a measurement line evaluation unit (23, 33) configured to estimate a quantitative error and/or to determine possibility of analysis, for analysis using measurement lines which are secondary X-rays of which the intensities are to be measured; and a display control unit (22, 32) configured to cause a display to display the quantitative error and/or the possibility of analysis obtained by the measurement line evaluation unit (23, 33), wherein the measurement line evaluation unit (23, 33) is configured to calculate, for all specified measurement lines, estimated measured intensities by theoretical intensity calculation and apparatus sensitivity on the basis of a composition and/or a thickness specified for the thin film, characterized in that the measurement line evaluation unit (23, 33) is configured to repeat a process of, on the basis of a set of estimated measured intensities obtained by changing, by a predetermined amount, only an estimated measured intensity of one measurement line among a set of the calculated estimated measured intensities, obtaining quantitative values of the composition and/or the thickness of the thin film after change of the estimated measured intensity by the fundamental parameter method, while changing a measurement line of which the estimated measured intensity is to be changed, and is configured to estimate the quantitative error and/or determines the possibility of analysis, on the basis of the obtained quantitative values and the specified composition and/or the specified thickness. a) a single-layer thin film formed without a substrate, or b) a multi-layer thin film formed without a substrate, or c) a single-layer thin film formed on a substrate, or d) a multi-layer thin film formed on a substrate, a measurement line evaluation unit (23, 33) configured to estimate a quantitative error and/or to determine possibility of analysis, for analysis using measurement lines which are secondary X-rays of which the intensities are to be measured; and a display control unit (22, 32) configured to cause a display to display the quantitative error and/or the possibility of analysis obtained by the measurement line evaluation unit (23, 33), wherein the measurement line evaluation unit (23, 33) is configured to calculate, for all specified measurement lines, estimated measured intensities by theoretical intensity calculation and apparatus sensitivity on the basis of a composition and/or a thickness specified for the thin film, characterized in that the measurement line evaluation unit (23, 33) is configured to repeat a process of, on the basis of a set of estimated measured intensities obtained by changing, by a predetermined amount, only an estimated measured intensity of one measurement line among a set of the calculated estimated measured intensities, obtaining quantitative values of the composition and/or the thickness of the thin film after change of the estimated measured intensity by the fundamental parameter method, while changing a measurement line of which the estimated measured intensity is to be changed, and is configured to estimate the quantitative error and/or determines the possibility of analysis, on the basis of the obtained quantitative values and the specified composition and/or the specified thickness. is configured to calculate, for all specified measurement lines, estimated measured intensities by theoretical intensity calculation and apparatus sensitivity on the basis of a composition and/or a thickness specified for the thin film, characterized in that the measurement line evaluation unit (23, 33) is configured to repeat a process of, on the basis of a set of estimated measured intensities obtained by changing, by a predetermined amount, only an estimated measured intensity of one measurement line among a set of the calculated estimated measured intensities, obtaining quantitative values of the composition and/or the thickness of the thin film after change of the estimated measured intensity by the fundamental parameter method, while changing a measurement line of which the estimated measured intensity is to be changed, and is configured to estimate the quantitative error and/or determines the possibility of analysis, on the basis of the obtained quantitative values and the specified composition and/or the specified thickness.