Abstract: The device for measuring the oxygen content in a gas mixture comprises three flow channels, a main channel, a measuring channel and a reference channel, over which the gas stream is distributed. By using a non-homogeneous magnetic field produced by a magnet, the gas flow is deflected into the measuring channel as a function of oxygen content; at the same time, the flow in the reference channel is reduced. The oxygen content of the gas is determined by means of a flow measurement of the volume flow of gas in the measuring or reference channel by means of resistance thermometers.