Disclosed herein is a measuring apparatus equipped with a plurality of measuring units. Each measuring unit includes a dielectric block, a thin film layer formed on the dielectric block, and a sample holding mechanism for holding a sample on the thin film layer. The measuring apparatus is further equipped with an optical system for making a light beam enter the dielectric block at an angle of incidence so that a total internal reflection condition is satisfied at an interface between the dielectric block and the thin film layer, and photodetectors for measuring the intensity of the light beam totally reflected at the interface. The optical system is constructed so that light beams simultaneously enter the dielectric blocks of the measuring units. The number of photodetectors corresponds to the number of the light beams.