To provide a pump device which hardly receives the environment of a mounting surface, and is hardly corroded in the pump device in which a pump is loaded on the upper part of a pressure tank, and is covered with a pump cover, by fitting a resin-made base in the lower part of the pressure tank.

In a pump device in which a pump 1 and the other main parts are loaded on the upper part of a pressure tank 2, liquid lifted by the pump 1 is introduced from a suction flange 14 to the pump 1, and water is fed from a discharge flange 15 through the pressure tank 2. The pressure tank 2 made of a steel plate is arranged for smoothening the automatic operation of a pump by compression/expansion of enclosed air accompanied by the starting/stopping of the pump accompanied by the opening/closing of a faucet. A resin base 12 having a base groove along the shape of a lower end, is annexed to the lower part of the thus arranged pressure tank 2. Hereby, this pump device hardly receives the environment of a mounting surface 5, especially hardly receives the influence of a water content, and can be prevented from being corroded from the lower end of the pressure tank 2.