A breast pump for pumping down breast milk, with a cylindrical hollow piston with at least one deepening circulating on the outside on the lower end with respect to the cylindrical superficies surface of the hollow piston, a suction cup, which is connected to the tipper end of the hollow piston via a passage for fluid, a soft elastic compensation element (8) between the hollow piston and the bearing surface of the suction cup, at least one circulating sealing element made of a soft elastic material, inserted into the deepening, and a cylinder with a closed lower end, in which the hollow piston is axially movable, wherein the superficies surface of the hollow piston is guided on an inner wall of the cylinder, the sealing element is sealingly arranged between the inner wall of the cylinder and the hollow piston, and at least the suction cup is arranged outside of the cylinder.
