NOVELTY - An infrared optical gas analyzer has cuvette (12) containing gas mixture; first multispectral detector (1) containing ray-mixing system in form of pyramid system; first infrared optical radiation source (6) positioned such that radiation emitted in first wavelength range reaches the first detector through interior space of cuvette; and pneumatic diaphragm arranged between 2 paths of rays integrated in the cuvette.    USE - Used for determining gas concentrations.    ADVANTAGE - The invention has compact design not prone to interference, and makes possible simultaneous measurement and identification of gases in gas mixture.    DETAILED DESCRIPTION - The infrared optical gas analyzer comprises cuvette containing gas mixture; first multispectral detector containing ray-mixing system in form of pyramid system; first infrared optical radiation source positioned such that radiation emitted in first wavelength range reaches the first detector through interior space of cuvette; second multispectral detector (2) containing the ray-mixing system; second radiation source (7) provided such that radiation emitted in a second wavelength range reaches the second detector through interior space of the cuvette, the first and second wavelength ranges are selected such that they will be different from one another; and pneumatic diaphragm arranged between 2 paths of rays integrated in the cuvette.    An INDEPENDENT CLAIM is also included for a process for determining gas concentrations with the infrared optical gas analyzer comprising providing first and second infrared optical radiation sources; providing first multispectral detector; providing second multispectral detector; providing cuvette with integrated pneumatic diaphragm arranged between the two paths of rays, the cuvette containing the gas mixture to be measured; positioning the optical radiation source such that the radiation emitted in a first wavelength range reaches the first multispectral detector through the interior space of the cuvette and radiation emitted in a second wavelength range reaches the second multispectral detector through the interior space of the cuvette; selecting the first and second wavelength ranges such that they will be different from one another; sending the radiation received by the first multispectral detector in the first wavelength range and sending the radiation received by the second multispectral detector in the second wavelength range as signals to an evaluating and control unit; and calculating at the evaluating and control unit values for the concentrations of a first group of gases contained in the gas mixture from the signals of the radiation in the first wavelength range, which are received by the first multispectral detector; calculating at the evaluating and control unit values for the concentrations of a second group of gases contained in the gas mixture from the signals of the radiation in the second wavelength range, which are received by the second multispectral detector.    DESCRIPTION OF DRAWING(S) - The figure is a schematic view showing the inventive gas analyzer with 2 paths of rays of equal length extending in parallel in a lateral cross-section.    First multispectral detector (1)    Second multispectral detector (2)    First radiation source (6)    Second radiation source (7)    Cuvette (12)