A device for humidifying breathing air for artificial respiration of mammals, in particular human beings, includes at least one essentially closed container for receiving water, a first opening for letting in the non-humidified air and a second opening for letting out humidified air, and an inlet for supplying the water to the container. The inlet is located in the upper part of the container, which is adjoined by a tube essentially crossing through the container interior, and on the free end of the tube, a valve is disposed, which limits the level of the water supplied via the tube in such a way that the container bottom in the container interior is essentially covered with water.