Abstract: In a diaphragm pump apparatus having a first chamber and a second chamber divided from the first by a movable diaphragm, the diaphragm comprises on both sides annular surfaces, whereby the annular surface is rounded out and goes over into a conically tapering thickened area and the other annular surface is provided with a concavely curved rounded-out portion incorporated into the thickened area of the diaphragm. By means of this design it is achieved that even highly viscous media can be pumped with the diaphragm pump apparatus, that the diaphragm has a long lifespan and that trouble-free operation of the diaphragm pump apparatus is ensured.