Patent ID: 7075657

Claim:
A measuring apparatus comprising: a measuring chip comprising a dielectric block portion, a thin film layer formed on one surface of said dielectric block portion, and a sample holding mechanism for holding a sample on a surface of said thin film layer; a light source for emitting a light beam; an optical incidence system for causing said light beam to enter said dielectric block portion at angles of incidence so that a total internal reflection condition is satisfied at an interface between said dielectric block portion and said thin film layer; photodetection means, which comprises a plurality of light-receiving elements, for detecting intensities of said light beam whose incidence angles are different, totally reflected at said interface; differentiation means for differentiating an optical detection signal output from each of the light-receiving elements of said photodetection means, in a direction where said light-receiving elements are juxtaposed, at intervals of outputs of two adjacent light-receiving elements; and computation means for specifying a reference light-receiving element by a predetermined method, then judging whether or not values of the optical detection signals of a first predetermined number of light-receiving elements increase monotonously in directions going to both sides with said reference light-receiving element as center, and computing a position of a dark line, contained in said light beam reflected at said interface, on the basis of a value obtained by differentiating the outputs of a second predetermined number of light-receiving elements sandwiching said reference light-receiving element when it is judged that the values of the optical detection signals increase monotonously, in said direction where said light-receiving elements are juxtaposed.