An optical chamber for a gas detection device, which includes reflecting device for reflecting radiation issued from a radiation source and for redirecting the radiation toward a radiation detector, the reflecting device including a first series of adjacent mirrors and a second series of adjacent mirrors. The mirrors of the first series and the mirrors of the second series are of the truncated ellipsoid of revolution type. The first series of mirrors and the second series of mirrors are arranged relative to each other so that the radiation emitted by the radiation source is reflected alternatively by a mirror of the second series and by a mirror of the first series and defines an optical path extending from the radiation source to the radiation detector.