The piston sampler ranks amongst those samplers which remove a selective sample from the material flow. To be able to secure sufficient representativeness, the product flows to be sampled must be homogeneous in terms of the various grain sizes. Sampling is carried out by means of a sample collecting pipe protruding in the material flow. This sample collecting pipe is provided with an opening, into which the material can drop permanently. At the time of sampling, a pneumatically actuated piston is pressed from the waiting position in the direction of the material flow by the sample collecting pipe. The sample collecting pipe is emptied over the material flow to then, on the return, take along the sample material just dropped in. The sample material can be taken over at a pipe socket outside the main pipe.