PURPOSE: To obtain a collecting device with a simple constitution and easy to handle by a method wherein a flexible cylindrical sheet member is installed at collecting ports of two pipes having different diameters and interlocking with each other so that each collecting port may be closed by those relative rotation.

CONSTITUTION: Two pipes 10, 11 having different diameters are interlocked so as to rotate in a relatively free way. At collecting ports 10, 11 of these two pipes, the both end opening parts of a cylindrical closing member 13 consisting of a flexible sheet closing each collecting port being throttled by the relative rotation of those pipes are installed, respectively. Accordingly, when a continuous sampling from a liquid level is performed, pipes 10, 11 are inserted up to the given depth keeping the closing member 13 in an opened state and pipes 10 and 11 are rotated mutually to a reverse direction to throttle the closing member 13. The pipes are pulled up while keeping said state and muddy water is collected from the inside of an inner pipe 11. In this way, a collecting device having a simple constitution and easy to handle is obtained.