In a surface plasmon resonance sensor, a sensor unit includes a dielectric block, a thin film layer which is formed on the upper surface of the dielectric block, and a sample holding portion. An incubator is provided, the surface plasmon resonance sensor is spatially isolated from the surroundings by placing it in the measuring system, the temperature of the measuring system is measured and temperature change of the sensor unit after it is conveyed to the measuring system from the incubator is estimated on the basis of the temperature difference between the temperature of the incubator and the temperature of the measuring system, and the sensor unit is conveyed to the measuring system to perform the measurement within a time for which the temperature of the sensor unit does not unacceptably change.