To provide a new technique capable of achieving miniaturization of a nitrogen substitution type deoxygenation device and also of efficiently, stably obtaining a deoxygenated water.

There is provided a deoxygenation device for reducing the dissolved oxygen in water by replacing the dissolved oxygen in water with nitrogen. The device includes at least: a water circulation unit for circulating the water stored in the tank in the deoxygenation device; a nitrogen gas injection part for injecting the nitrogen gas into the water; a nitrogen gas mixing part for mixing the nitrogen gas in the water; and a flow adjuster, provided between the nitrogen gas injection part and the tank, for adjusting the flow of a circulating water. The pressure of the outlet of the water circulation unit is controlled by the flow adjuster so as to be 0.1-0.6 MPa.