In order to secure a separation ability required for an oxidation catalyst such as a non-methane cutter, and to enable a sample gas to be measured accurately, this gas analyzing device is provided with a sample gas line where a sample gas flows, an analyzer that is provided in the sample gas line and that detects the concentration of a specific component contained in the sample gas, a catalyst that is arranged upstream of the analyzer in the sample gas line and that reacts with the sample gas, and a moisture concentration adjusting unit that is arranged upstream of the catalyst in the sample gas line to adjust the moisture concentration of the sample gas.