A gas analyzer includes an optical emitter that irradiates measurement light into a measurement region including a measured-gas, a first optical receiver that receives the measurement light passing through the measurement region, a splitting unit between the optical emitter and the measurement region that splits off a portion of the measurement light irradiated from the optical emitter to yield reference light, a reference unit, and an optical component. The reference unit holds a gas containing a measurement target component identical with the measured-gas but at a known concentration and a second optical receiver that receives the reference light passing through the region including the gas. The optical component is disposed between the splitting unit and the region and expands the beam diameter of the reference light to be larger at the second optical receiver than the receiving diameter of the second optical receiver.