A measuring cell is formed of base plates joined together. A passage groove is formed on a joining surface of one base plate. Through-holes for introducing and discharging a fluid sample are formed on the other base plate, and the joining surface is provided with an optically opaque Si film as slits. Further, the joining surfaces of the base plates and the inner surface of the passage groove are covered with SiO2 films. Thus, a measuring cell having a sufficiently small passage sectional area, a high air-tightness, a chemically stable measuring chamber, and a high measuring sensitivity can be obtained.