To provide a pump device capable of maintaining a pulsation- preventing function for a long time period.

In a pump device, a diaphragm 200 made of a rubber and closing a communication passage 110 connecting a gas separation device 60 and a fluid discharge passage 30 is provided. When a pulsation is generated in the fluid discharge passage 30, the diaphragm 200 receives the pulsation and is deflected and deformed and the pulsation is absorbed by the deformation. Therefore, it is inhibited that the pulsation is transmitted to a gas/liquid separation device 31 provided at a latter stage of a pump 19, a filter 41 a flow meter connected to a discharge opening 12, a nozzle, etc., and a generation of an erroneous operation caused by the pulsation of these connection members. Even if a hole is tentatively generated on the diaphragm due to a secular deterioration, since the pulsation is absorbed by the deflection and deformation of a whole surface of the diaphragm 200, a pulsation-preventing function is not immediately lost and the pulsation-preventing function can be exhibited for a long time period.