A quantitative analysis method, which is performed by an X-ray fluorescence spectrometer, the quantitative analysis method comprising: a step of acquiring a plurality of X-ray fluorescence spectra at least having a first peak at a first energy position from a sample containing a plurality of elements under different measurement conditions comprising different excitation energies; a step of designating, from among the plurality of spectra, a primary spectrum having the first peak and a secondary spectrum having the first peak and a second peak at a second energy position, wherein the second energy position differs from the first energy position, and wherein the first peak is generated by a first element and the second peak is generated by a second element of the sample; a first fitting step of performing a fitting on the first peak of the secondary spectrum to calculate a background intensity at the second energy position due to the first peak, wherein the first fitting step includes calculating a content of the first element and calculating the background intensity at the second energy position based on the content of the first element; and a second fitting step of performing a fitting on the first peak of the primary spectrum and performing a fitting on the second peak of the secondary spectrum under a condition that the calculated background intensity is included at the second energy position, wherein the second fitting step includes calculating a content at which a theoretical profile for the second peak of the secondary spectrum based on the calculated background intensity fits a spectrum of the second peak of the secondary spectrum, and a theoretical profile for the first peak of the primary spectrum fits a spectrum of the first peak of the primary spectrum. a step of acquiring a plurality of X-ray fluorescence spectra at least having a first peak at a first energy position from a sample containing a plurality of elements under different measurement conditions comprising different excitation energies; a step of designating, from among the plurality of spectra, a primary spectrum having the first peak and a secondary spectrum having the first peak and a second peak at a second energy position, wherein the second energy position differs from the first energy position, and wherein the first peak is generated by a first element and the second peak is generated by a second element of the sample; a first fitting step of performing a fitting on the first peak of the secondary spectrum to calculate a background intensity at the second energy position due to the first peak, wherein the first fitting step includes calculating a content of the first element and calculating the background intensity at the second energy position based on the content of the first element; and a second fitting step of performing a fitting on the first peak of the primary spectrum and performing a fitting on the second peak of the secondary spectrum under a condition that the calculated background intensity is included at the second energy position, wherein the second fitting step includes calculating a content at which a theoretical profile for the second peak of the secondary spectrum based on the calculated background intensity fits a spectrum of the second peak of the secondary spectrum, and a theoretical profile for the first peak of the primary spectrum fits a spectrum of the first peak of the primary spectrum.