An analysis chip comprises a thin film layer, which is formed on a dielectric material block and has two different regions. A flow path unit comprising a supply path for supplying a sample onto the thin film layer and a discharging path for discharging the sample is releasably loaded into the analysis chip. A light beam is irradiated to a first interface between one region of the thin film layer and the dielectric material block, and a second interface between the other region of the thin film layer and the dielectric material block, in a parallel manner. Refractive index information with regard to a substance to be analyzed, which is located on the thin film layer, is acquired from intensities of the light beam totally reflected from the first interface and the light beam totally reflected from the second interface.