A dioxin analyzing method sensitively detecting dioxins is provided. The method includes the first step of obtaining respective specific wavelength spectra of a plurality of dioxin isomers whose concentrations are known, selecting a plurality of specific wavelengths from each of the specific wavelength spectra, and preparing calibration curves, each showing the relationship between the ion signal intensity and the dioxin isomer concentration at any one of the selected specific wavelengths, for all the specific wavelengths selected for each dioxin isomer; the second step of preparing a sensitivity matrix showing the relationship between the ion signal intensities and the dioxin isomer concentrations at the specific wavelengths, from the calibration curves of the dioxin isomers prepared in the first step; and the third step of obtaining a specific wavelength spectrum of a sample to be analyzed, and determining the concentrations of a plurality of dioxin isomers in the sample using the ion signal intensities of the specific wavelength spectrum and the sensitivity matrix prepared in the second step.