PURPOSE: To realize smooth start of pump and instantaneous exhaustion of the passage and facilitate the repetitive samplings, by attaching a valve which can open the passage to the atomosphere.

CONSTITUTION: The sample air is sucked by an air pump 2 through a sampling port 1, and is sent into a sample container 5 by way of valve 6, flow regulator 3 and flow meter 4. When the valve 6 is changed to state A as shown by dotted line, bing open to the atmosphere, the pump 2 may be started up smoothly without having resistance of regulator 3 or the like. After the start-up, when the valve 6 is changed in the direction of solid line, the sample will flow into the container 5. To repeat sampling, by changing the valve 6 over to state A after sampling by a specified amount for a specified time, the sample staying in the passage will be opened to the atmosphere instantly, so that the pump 2 may start smoothly. Then, switching the valve 6 in the direction of solid line, sampling to a new container 5 may be repeated