A spectrometric analyzing device is capable of analyzing a thin film with high accuracy by using light having an arbitrary wavelength, such as not only infrared light but also visible light, ultraviolet light and X-ray, and using whatever refractive index of a supporting member of the thin film. A spectrometric analyzing device comprises a light source (1), a polarizing filter (2), a detection unit (3), a regression operation unit (4) and an absorbance spectrum calculation unit (5). The light source (1) emits light at n different angles of incidence (θn) to a measurement portion. The polarizing filter (2) shields an s-polarized component. The detection unit (3) detects transmitted spectra (S). The regression operation unit (4) uses the transmitted spectra (S) and a mixing ratio (R) to obtain an in-plane mode spectrum (sip) and an out-of-plane mode spectrum (sop) through a regression analysis. The absorbance spectrum calculation unit (5) calculates an in-plane mode absorbance spectrum (Aip) and an out-of-plane mode absorbance spectrum (Aop) of the thin film, based on the results from a state in which the thin film is on the supporting member and a state in which no thin film is on the supporting member.