A simple and convenient sensor and measuring apparatus utilizing the optical interference effect of an optical thin film capable of measuring the binding between biochemical substances at a high throughput and having alkali resistance. An optical thin film of silicon nitride is disposed on the first surface and the rear surface of a silicon substrate, and the thickness of the silicon nitride film is modified in a direction parallel to the film. A portion of the thin film with increased thickness is used as a sensor upon which a probe is disposed, and over which a sample-containing solution is caused to flow. The binding between the probe and biochemical sample is detected based upon the change of the intensity of reflected light.