A gas analyzer capable of measuring a concentration of a gas component in gas at sensor units provided at a plurality of positions in real time by decreasing the number of signals input from the sensor units to an analyzer so as to reduce a data amount input to the analyzer and a gas analyzing method. The gas analyzing method includes the steps of: demultiplexing laser light by a demultiplexer into measurement laser light and reference laser light; letting the measurement laser light pass through gas to be received by a photoreceiver; finding an absorption spectrum absorbed by a gas component in the gas based on a light intensity of the received measurement laser light and of the reference laser light; and analyzing the absorption spectrum to measure a concentration of the gas component.