PURPOSE: To prevent contamination of an atmosphere of a sample, by combining a flow path switching valve and a sample flow path switching valve, usually returning the sample to a collecting point, and discharging it into the air only at the time of quantitative analysis of the sample.

CONSTITUTION: A sample passes through a sample quantitative analyzer 7 from a sample inlet 1 of a flow rate switching valve 6, and flows to a collecting point through a sample outlet 2. In this case, the sample in the sample quantitative analyzer 7 becomes pressure of the collecting point, therefore, when pressure of the collecting point is varied by an operating condition of a plant, etc., capacity of the sample held in the sample quantitative analyzer 7 is also varied, and reproducibility of the sample quantitative analysis is bad. Therefore, by switching the sample flow rate switching valve, discharge of the sample is changed to the sample outlet 3 and it is discharged into the air. In this state, the sample in the sample vessel 7 becomes nearly atmospheric pressure, and constant capacity is held. When a sample switching valve 8 is switched, carrier gas goes in from a carrier gas inlet 4, and the sample of a constant quantity in the quantitative analyzer 7 flows to an outlet 5 through a separating column 9 and a detector 10. Accordingly, contamination of an atmosphere by the sample is prevented.