An oxygen concentration device and an oxygen concentration method are capable of arbitrarily adjusting the concentration of an oxygen gas to be supplied to an anesthesia machine in a range of about 25 to 90% using an oxygen concentrator used for an ordinary oxygen treatment. An oxygen concentration device includes: a compressor configured to supply atmospheric air； oxygen concentration units configured to generate concentrated oxygen from the air supplied by the compressor； and a flow rate adjustment unit configured to purge a part of the concentrated oxygen suppliable from the oxygen concentration units to an anesthesia machine into the atmosphere, wherein the flow rate adjustment unit adjusts a flow rate of the concentrated oxygen to be purged into the atmosphere to control an oxygen concentration of the concentrated oxygen to be supplied to the anesthesia machine.
