A pumping device includes a barrel, a top cover mounted on an open top of the barrel, a cylinder mounted in the barrel and connected to the top cover, a piston movably mounted in the cylinder, a plurality of check valves mounted on the piston, an operation unit mounted on the top cover and connected with the piston, a connecting unit mounted in the barrel and connected between the barrel and the cylinder, and a pressure adjusting unit connected between the barrel and the top cover. Thus, when the air pressure in the receiving chamber of the barrel reaches a predetermined value, the pressure adjusting unit provides a pressure release function to partially release the air pressure in the receiving chamber of the barrel so as to ensure a safe operation of the pumping device.