The invention concerns an apparatus for supplying a respiratory gas and a method of controlling the apparatus. In accordance with the invention there is provided an apparatus for supplying a respiratory gas comprising a conveyor device for conveying the respiratory gas, a conduit means for feeding the respiratory gas conveyed by the conveyor device to a person, and a humidification device for humidifying the respiratory gas, which is distinguished by a sensor device for generating a signal indicative in respect of the respiratory gas humidity and a control device for controlling the humidification device having regard to the signal which is generated by the sensor device and which is indicative in respect of the respiratory gas humidity. Furthermore there is proposed a method of supplying a respiratory gas to a patient, in which the respiratory gas is introduced by means of a conveyor device into a conduit system leading to a patient and is humidified, wherein the conveyor device is operated in such a way that a respiratory gas pressure which is above ambient pressure obtains in the air conduit system, which is distinguished in that signals indicative in respect of the relative and/or absolute humidity of the respiratory gas are generated by means of a sensor device and the humidity of the respiratory gas is adjusted on the basis of the signals generated in that way.