A quantitative analysis method, which is performed by an X-ray fluorescence spectrometer, includes: a step of acquiring a plurality of spectra at least having a first peak at a first energy position from a sample containing a plurality of elements under different measurement conditions; a step of designating, from among the plurality of spectra, a primary spectrum and a secondary spectrum having a second peak at a second energy position; a first fitting step of performing a fitting on the first peak included in the secondary spectrum to calculate a background intensity at the second energy position due to the first peak; 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.