An X-ray analysis system, comprising: an X-ray spectrometer; and a vapor phase decomposition apparatus, wherein the X-ray spectrometer includes: an X-ray source configured to irradiate a measurement sample having a thin film present on a surface of the measurement sample with primary X-rays; a detector configured to measure an intensity of reflected X-rays obtained when the primary X-rays are reflected by the surface or an interface of the measurement sample, or an intensity of fluorescent X-rays generated by the primary X-rays; and a calculation unit configured to calculate a film thickness or a coating mass of the thin film based on the intensity of the reflected X-rays or the fluorescent X-rays, and further configured to calculate a density of the thin film, and wherein the vapor phase decomposition apparatus includes: a vapor phase decomposition portion configured to perform vapor phase decomposition on the thin film; and a control portion configured to determine a vapor phase decomposition time based on the film thickness or the coating mass calculated by the calculation unit, and further configured to correct, based on the density, the determined vapor phase decomposition time. an X-ray spectrometer; and a vapor phase decomposition apparatus, wherein the X-ray spectrometer includes: an X-ray source configured to irradiate a measurement sample having a thin film present on a surface of the measurement sample with primary X-rays; a detector configured to measure an intensity of reflected X-rays obtained when the primary X-rays are reflected by the surface or an interface of the measurement sample, or an intensity of fluorescent X-rays generated by the primary X-rays; and a calculation unit configured to calculate a film thickness or a coating mass of the thin film based on the intensity of the reflected X-rays or the fluorescent X-rays, and further configured to calculate a density of the thin film, and an X-ray source configured to irradiate a measurement sample having a thin film present on a surface of the measurement sample with primary X-rays; a detector configured to measure an intensity of reflected X-rays obtained when the primary X-rays are reflected by the surface or an interface of the measurement sample, or an intensity of fluorescent X-rays generated by the primary X-rays; and a calculation unit configured to calculate a film thickness or a coating mass of the thin film based on the intensity of the reflected X-rays or the fluorescent X-rays, and further configured to calculate a density of the thin film, and wherein the vapor phase decomposition apparatus includes: a vapor phase decomposition portion configured to perform vapor phase decomposition on the thin film; and a control portion configured to determine a vapor phase decomposition time based on the film thickness or the coating mass calculated by the calculation unit, and further configured to correct, based on the density, the determined vapor phase decomposition time. a vapor phase decomposition portion configured to perform vapor phase decomposition on the thin film; and a control portion configured to determine a vapor phase decomposition time based on the film thickness or the coating mass calculated by the calculation unit, and further configured to correct, based on the density, the determined vapor phase decomposition time.