A spectral analysis device for use in analyzing the molecular orientation of a thin film, said spectral analysis device comprising: a light source capable of emitting light having a plurality of predetermined wavelengths; a support body that is optically transparent to the light emitted from the light source and is configured to support a thin film to be analyzed, the support body being fixed such that an incident angle of the light emitted from the light source to the support body is a predetermined incident angle θ specific to the support body; a linear polarization filter disposed between the light source and the support body, the linear polarization filter being able to change a polarization angle such that lights with n (n = 3, 4,...) different polarization angles φ n of arbitrary intervals ranging from 0° to 90° are irradiated to the support body; a detection unit for detecting a transmitted spectrum matrix S collecting each transmitted spectrum s obs detected for each polarization angle φ n by receiving each of transmitted lights in which the lights with the n different polarization angles φ n by the linear polarization filter are transmitted through the support body and the thin film; a regression computation unit configured to obtain an in-plane spectrum s ip, which is a spectrum obtained when ordinary light having an electric field oscillation perpendicular to a traveling direction of the light is subjected to normal-incidence transmission measurements, and an out-of-plane spectrum s op, which is a spectrum obtained when virtual light having an electric field oscillation in a traveling direction of the light is subjected to normal-incidence transmission measurements, through regression analysis by using the transmitted spectrum matrix S detected by the detection unit and a mixing ratio R of the in-plane spectrum s ip and the out-of-plane spectrum s op for each polarization angle; and an absorbance spectrum calculation unit for calculating an in-plane absorbance spectrum A ip and an out-of-plane absorbance spectrum A op of the thin film based on the in-plane spectrum s ip and the out-of-plane spectrum s op each obtained by the regression computation unit for each of a state where the thin film is supported on the support body and a state where the thin film is not supported on the support body. a light source capable of emitting light having a plurality of predetermined wavelengths; a support body that is optically transparent to the light emitted from the light source and is configured to support a thin film to be analyzed, the support body being fixed such that an incident angle of the light emitted from the light source to the support body is a predetermined incident angle θ specific to the support body; a linear polarization filter disposed between the light source and the support body, the linear polarization filter being able to change a polarization angle such that lights with n (n = 3, 4,...) different polarization angles φ n of arbitrary intervals ranging from 0° to 90° are irradiated to the support body; a detection unit for detecting a transmitted spectrum matrix S collecting each transmitted spectrum s obs detected for each polarization angle φ n by receiving each of transmitted lights in which the lights with the n different polarization angles φ n by the linear polarization filter are transmitted through the support body and the thin film; a regression computation unit configured to obtain an in-plane spectrum s ip, which is a spectrum obtained when ordinary light having an electric field oscillation perpendicular to a traveling direction of the light is subjected to normal-incidence transmission measurements, and an out-of-plane spectrum s op, which is a spectrum obtained when virtual light having an electric field oscillation in a traveling direction of the light is subjected to normal-incidence transmission measurements, through regression analysis by using the transmitted spectrum matrix S detected by the detection unit and a mixing ratio R of the in-plane spectrum s ip and the out-of-plane spectrum s op for each polarization angle; and an absorbance spectrum calculation unit for calculating an in-plane absorbance spectrum A ip and an out-of-plane absorbance spectrum A op of the thin film based on the in-plane spectrum s ip and the out-of-plane spectrum s op each obtained by the regression computation unit for each of a state where the thin film is supported on the support body and a state where the thin film is not supported on the support body.