In a diaphragm pump flap valves accommodated in a pump head are provided which have a valve disk in which are situated valve flaps (14) circumscribed by partial ring-shaped recesses. These are respectively flexibly connected with the remaining valve disk (15) by means of a web (17). The valve disk is clamped between pump head elements in an area circumscribing each respective valve. In order to avoid material displacements and deformations resulting from the clamping from acting upon the web and the valve flap (14), it is provided that an opening (19) of the valve disk (15) is situated in a connecting area between valve flap (14), web (17) and outer clamping (18), facing away from the valve flap (14). Material displacements originating from the clamping area (18) can thereby no longer influence the valve flap (14) and the web (17), since a transmission of these material deformations is interrupted in the area of the opening (19).