A total reflection illuminated sensor chip is employed in a detecting method for detecting a detection target substance including the steps of: supplying a sample that includes the detection target substance onto a metal film formed on a surface of a dielectric prism, irradiating a measuring light beam onto the interface between the dielectric prism and the metal film such that conditions for total reflection are satisfied at the interface, and utilizing evanescent waves which are generated due to the irradiation of the measuring light beam to detect the detection target substance. Polishing streaks in the region of a metal film formation surface of the dielectric film, on which the metal film is formed, have directional properties with respect to a single direction.