To effectively reduce a measurement error in a parameter indicating a state of spectroscopic polarization generated by variations in retardation of a retarder due to a temperature change or other factors, while holding a variety of properties of a channeled spectroscopic polarimeter. By noting that reference phase functions .phi..sub.1(.sigma.) and .phi..sub.2(.sigma.) are obtained by solving an equation from each vibration component contained in a channeled spectrum P(.sigma.), the reference phase functions .phi..sub.1(.sigma.) and .phi..sub.2(.sigma.) are calibrated concurrently with measurement of spectrometric Stokes parameters S.sub.0(.sigma.), S.sub.1(.sigma.), S.sub.2(.sigma.), and S.sub.3(.sigma.).