Abstract: An apparatus for preparing gas mixtures from constituents taken in a given proportion which incorporates sources of gas mixture constituents connected to pressure-reducing valves and to a device for stabilizing absolute pressures of the gas mixture constituents an outlet of which communicates with a device for setting a proportion between the gas mixture constituents consisting of a distributor which is series-connected to at least two--depending on the number of the gas mixture constituents--sets of capillary tubes featuring all the same friction head. The device for setting the proportion between the gas mixture constituents is connected to a main mixer of the gas mixture components an outlet of which communicates with a controller of absolute pressure of the gas mixture.