To provide an oxygen concentration device by which the leakage stage of oxygen-concentrated gas in a humidifier, etc., can surely be grasped.

At a step 100, an electromagnetic valve is driven to temporarily cut off the channel of the oxygen-concentrated gas. At a step 110, in order to stabilize the state of the flow, etc., of the oxygen-concentrated gas, the device waits for a prescribed period (2 to 3 sec, e.g.). At a step 120, the pressure P of the oxygen-concentrated gas is detected by a pressure sensor. At a step 130, it is decided whether the pressure P of the detected oxygen-concentrated gas becomes lower than a prescribed discrimination value KP, that is whether leakage occurs on the side of the humidifier. When it is decided to be YES, the step is advanced to a step 140. Since it is decided that leakage occurs on the side of the humidifier, an abnormality notification lamp is lighted (or flickered) and sound or voice is outputted to inform that leakage exists, at the step 140.