A gas concentration measuring apparatus utilizing a gas correlation method capable of measuring concentrations of a plurality of analyte gases simultaneously and at high sensitivity uses an infrared light source (2) such as an infrared semiconductor diode or a quantum cascade semiconductor laser to increase the intensity of collimated infrared light (5) and to lessen infrared light unnecessary for measurement, thereby improving the S/N ratio while achieving a rise in sensitivity. A plurality of analyte gases are simultaneously measured by means of a gas correlation filter comprising a reference gas cell (6a) filled with all of the analyte gases and a plurality of probe gas cells (6b) each individual of which is filled with all such analyte gases other than one of the analyte gases which is of its particular interest.