A gas analyzer includes: a first signal processing section for synchronously detecting a light detection signal at a frequency being an integral multiple of a modulation frequency fa of a laser light, to detect a harmonic signal intensity Signal(ν) by a harmonic synchronous detection method; a second signal processing section for capturing a light detection signal and cutting off a frequency component not smaller than the frequency fa to detect a light intensity signal I(ν) at a specific light frequency absorbed by a component to be measured in a sample gas; and an operation section. The operation section includes a first operation means for calculating a density c of the component from the harmonic signal intensity Signal(ν) and a reference light intensity signal I0(ν) and a second operation means for calculating the density c from the light intensity signal I(ν) and the reference light intensity signal I0(ν).