To shorten the measuring time of a measuring instrument utilizing the attenuated total reflectance caused by surface plasmon, etc., without lowering the measuring accuracy of the coupling between a sensing material and an object to be inspected.

A sample liquid 15 containing the object to be inspected is supplied to a measuring unit 10 in which the sensing material is fixed by means of a sample liquid supplying mechanism 70, and a light beam 30 is made incident to the unit 10 at various angles so that a total reflection conduction may be obtained on the interface between a metallic film 12 formed on the internal bottom face of the unit 10 and a dielectric block underlying the film 12. In this state, the light beam 30 totally reflected by the interface is detected by means of a photodetector 40 and the variation U(t) of the angle of attenuation total reflectance with time is found based on the detected value of the photodetector 40. After measurement is performed a plurality of times within 20 minutes, the measurement is terminated and the fitting parameters A and B of a prediction formula, U(t)=A(1-e-Bt), are decided. A measuring means 61 calculates the valuation U(t) until the longest predicting time of 120 minutes inputted from a time setting section 80 elapses based on the prediction formula, and displays the calculated variation U(t) on a displaying section 62.