PURPOSE: To obtain the highly relable result of measurement, by starting the measurement after confirmation that a sample attains a set temp.

CONSTITUTION: A constant temp. flow cell 1 provided in a thermost 10 is communicated with a sample vessel 2 and a pump 3 for sucking and discharging the sample. When the sample is heated up to the set temp. by a temp. control circuit 5, the attainment of the set temp. is detected by a monitor circuit 6, which in turn transmits a signal to a CPU7. The CPU transmits the signal for the attainment of the set temp. to a measurement circuit 8, then the circuit 8 starts measurement.