To provide an infrared gas analyzer capable of grasping quantitatively a light quantity drift of a light source due to deterioration of the light source, or the like, compensating a concentration signal drift of a measuring component, and performing high-accuracy measurements.

This infrared gas analyzer, having a measuring cell wherein sample gas is circulated for detecting the concentration of measuring component gas in the sample gas by utilizing a change of intensity of infrared light passing the measuring cell, is equipped with the light source controlled by a light source driving voltage control circuit for generating the infrared light; a measuring gas cell detection part for detecting the intensity of the infrared light passing the measuring cell; and the monitor gas cell detection part, to which the infrared light from the light source is guided for detecting an infrared ray absorption amount by gas other than the measuring component gas in the guided infrared light. The monitor gas cell detection part determines the deviation between a signal that detects the absorbed amount by gas other than the measuring component gas and a value set beforehand, and feedbacks a controlled variable based on the determined deviation amount to the light source drive voltage control circuit.