Abstract: An infrared gas analyzer is formed of a source of infrared rays for emitting infrared flux; an infrared flux interrupting device for chopping the emitted infrared flux from the source of the infrared rays; a condensing optical system for obtaining a predetermined solid angle in the emitted infrared flux to thereby form a condensed flux; and a multi-reflection cell disposed at an outlet of the condensing optical system, to which the condensed flux is supplied and a gas to be measured is fed. The multi-reflection cell has a multi-reflection optical system formed of a plurality of concave mirrors. The analyzer also includes an infrared level detector for detecting an amount of infrared rays with a wavelength band absorbed by a component gas to be analyzed and contained in the infrared rays emitted by the multi-reflection cell.