The non-dispersive gas analyser has a measuring vessel (5) which can be filled with a measuring gas and which can be irradiated by a measuring beam (3). The analyser also has at least one detector arranged outside the beam path. The beam reflecting inner wall of the measuring vessel (9) of the detector (10) is arranged behind an opening (11) in a side wall of the measuring vessel (5) parallel to the beam path at the smallest possible distance from the inner chamber of the measuring vessel (5). The measuring vessel (5) is formed without any beam splitting arrangement. The side wall (9) of the measuring vessel (5) may have a recess (12) or groove (12) around the opening (11) in which the detector (10) is arranged. The detector may be an optical-pneumatic detector.
