To fix a smaller quantity of specimen in a shorter time when fixing the same specimen to a plurality of sensor units.

A measuring instrument 11 is provided with a plurality of measurement stages 15 each comprising a prism and a flow path member 20. On each measurement stage 15, a sensor unit 12 is fixed by being sandwiched between the prism and the path member 20 to bring a flow path 16 into pressure contact with the sensor unit 12. A pipe 40 for injection is connected to an injection port 16a of each flow path 16 while a pipe 42 for discharge is connected to each discharge port 16b. Adjoining measurement stages 15 are connected to each other by a pipe 48 for communication via a pipe 42 for discharge on one side and a pipe 40 for injection on the other side. Since the sensor units 12 are serially connected via the pipes 48, it is made possible to bring a specimen into contact with the plurality of sensor units 12 by one time of liquid feed to fix the small quantity of specimen in a short time.