The present invention reliably eliminates the effect of measurement-disturbing components, improves the accuracy of measurement of components to be measured, and simultaneously measures a plurality of the components to be measured. Light from a light source is scanned in a specific scanning band by an interference filter (12) at a prescribed scanning frequency, and a sample liquid is irradiated with the light. Light that has passed through an optical cell (18) is converted by a light detector (20) into an electrical signal. To simultaneously quantify a plurality of types of the components to be measured that are contained in a sample, a processing device (22) uses: the strength of a plurality of harmonic components that have been obtained by performing fast Fourier transform on and computing the signal; and the correspondence relation between the plurality of types of components to be measured and the strength of the plurality of harmonic components, said correspondence relation having been measured in advanc
