The object of the invention is a device for supplying respiratory gas to a patient according to respiratory cycles, comprising a gaseous flow rate generator provided with a turbine with low inertia and high nominal speed, a first circuit called a supply circuit for the gaseous flow toward a respiratory mask or an intubation means of the patient, means for measuring pressure and/or measuring flow rate of the gaseous flow, computation means for parameters of pressure and/or flow rate, and means for controlling the speed of rotation of the generator, characterized in that the measuring means, the computation means and the speed control means coact automatically to control the speed of rotation of the turbine as a function of the inspiration and expiration phases and as a function of patient pressure signals and/or inspiration flow rate signals.