Abstract: A pneumatically controlled tamper includes a cylinder which has a lateral supply opening for compressed air and which is integral with a foot. A piston with a symmetrical structure possesses two internal channels provided with check valves. The first channel terminates at one end on the lateral surface of the piston, above its median plane, and at the other end at the bottom of the piston in a lower chamber connected to the atmosphere by an escape opening. The second channel terminates at one end on the lateral surface of the piston, below its median plane, and at the other end at the top of the piston, in an upper chamber connected to the atmosphere through another escape opening. When the piston is on the bottom of the cylinder, the supply opening supplies the first channel, this arrangement making it possible to initiate a reciprocating movement which is maintained without any distribution system. The invention is used preferentially for soil compacting.