To provide a pump device which can eliminate evacuation work for obtaining proper sealing water, and can improve the performance and the durability of the pump device.

The pump device 1 generates negative pressure in a separate tank 3 by using a vacuum pump 10, sucks water by the negative pressure into the separate tank 3 and pumps up it. Circulating water in a cooling water tank 4 is supplied to the vacuum pump 10 via a water supply pipe 21, used as the sealing water, and after that, returned to the cooling water tank 4 via a water discharge pipe 23. Since a water take-in port 13 of the vacuum pump 10 is arranged in a position lower than a water supply port H, the circulating water in the cooling water tank 4 flows out to the water supply pipe 21, the water supply pipe 21 and a water supply hose 22 are not mixed with air, the power of a motor 2 is not consumed at all due to the supply of the circulating water to the vacuum pump 10, and thus the performance of the pump device 1 is improved.