An opto-acoustic gas analyzer has a black body light source, a chopper in the path of the light emitted from the light source for intermittently intercepting the light from the light source, a positive interference filter in the path of the light for filtering out light other than the wavelengths of light absorbed by the gas being analyzed, and an opto-acoustic detector which receives the filtered light and through which the gas to be analyzed is passed. A pressure change detector provided is provided in the opto-acoustic detector for detecting pressure changes in the gas and producing an electric signal corresponding such changes.