To provide a dry air feed method capable of maintaining oxygen concentration of dry air in a predetermined range.

In this dry air feed method for feeding dry air to a dry air feed system by dehumidifying water contained in pressurized air by using a dehumidifier of polyimide-based hollow fiber separation membrane type, the dehumidifier feeds air to be dehumidified to the primary side of the polyimide-based hollow fiber separation membrane, feeds a part of obtained dry air to its secondary side as purge air, and regulates the flow rate of purge air so that the concentration of oxygen contained in the obtained dry air or the flow rate of dry air flowing from the primary side is not below the predetermined range.