<p>A gas analyzer comprising a light-source (1), a gas-passing through cell (2), a light-quantity detector (3) and a gas-distributor (4) for alternately introducing a sample gas and a reference gas into said gas-passing through cell at an appointed cycle and adapted to take out an alternating current component corresponding to a difference between an optical energy after passing through said reference gas and an optical energy after passing through said sample gas on the basis of an output signal from said light-quantity detector to determine a concentration of a component contained in said sample gas on the basis of a change of the alternating current component is characterized by compensating means (Y) for detecting a direct current component from the output signal from said light-quantity detector separately from said alternating current component and dividing said change of the alternating current component by said direct current component.</p>
