A measurement line evaluation unit (23): calculates, for all of specified measurement lines, estimated measured intensities by theoretical calculation on the basis of a composition and/or a thickness specified for a thin film; changes, by a predetermined amount, only an estimated measured intensity of one measurement line, and obtains quantitative values of the composition and/or the thickness of the thin film after change of the estimated measured intensity, for each changed measurement line, by a fundamental parameter method; and estimates a quantitative error and/or determines possibility of analysis, on the basis of the obtained quantitative values and the specified composition and/or the specified thickness.