A gas analyzer comprising: an optical emitter, suitable for measurements by tunable diode laser absorption spectroscopy, configured to irradiate measurement light into a measurement region including a measured-gas along an optical axis; an alignment mechanism configured to adjust an emission position of the measurement light irradiated from the optical emitter in a direction substantially orthogonal to the optical axis and the alignment mechanism having an alignment range and a standard position; a first optical receiver configured to receive the measurement light after the measurement light passes through the measurement region; a splitting unit disposed between the optical emitter and the measurement region and configured to split off a portion of the measurement light irradiated from the optical emitter to yield reference light; a reference unit comprising a reference cell comprising a condensing lens attached to an entrance face of the reference cell comprising a gas, identical to a measurement target component in the measured-gas, at a known concentration and a second optical receiver configured to receive the reference light after the reference light passes through a region of the reference unit including the gas; and an optical component disposed between the splitting unit and the region of the reference unit including the gas; wherein the condensing lens is configured such that the reference light would, in absence of the optical component and when the alignment mechanism is in its standard position, be focused in a focal point in the reference unit near the second optical receiver and the beam diameter of the reference light incident on the second optical receiver would be substantially equal to a receiving diameter of the second optical receiver, and wherein a focal length of the optical component is set to a value that allows the second optical receiver to receive the reference light over an alignment range in which the emission position of the measurement light in a direction orthogonal to an optical axis of the measurement light is adjusted by the alignment mechanism and that maximizes an irradiation intensity of the reference light; wherein the optical component is configured to expand a beam diameter of the reference light to be larger at the second optical receiver than the receiving diameter of the second optical receiver. an optical emitter, suitable for measurements by tunable diode laser absorption spectroscopy, configured to irradiate measurement light into a measurement region including a measured-gas along an optical axis; an alignment mechanism configured to adjust an emission position of the measurement light irradiated from the optical emitter in a direction substantially orthogonal to the optical axis and the alignment mechanism having an alignment range and a standard position; a first optical receiver configured to receive the measurement light after the measurement light passes through the measurement region; a splitting unit disposed between the optical emitter and the measurement region and configured to split off a portion of the measurement light irradiated from the optical emitter to yield reference light; a reference unit comprising a reference cell comprising a condensing lens attached to an entrance face of the reference cell comprising a gas, identical to a measurement target component in the measured-gas, at a known concentration and a second optical receiver configured to receive the reference light after the reference light passes through a region of the reference unit including the gas; and an optical component disposed between the splitting unit and the region of the reference unit including the gas; wherein the condensing lens is configured such that the reference light would, in absence of the optical component and when the alignment mechanism is in its standard position, be focused in a focal point in the reference unit near the second optical receiver and the beam diameter of the reference light incident on the second optical receiver would be substantially equal to a receiving diameter of the second optical receiver, and wherein a focal length of the optical component is set to a value that allows the second optical receiver to receive the reference light over an alignment range in which the emission position of the measurement light in a direction orthogonal to an optical axis of the measurement light is adjusted by the alignment mechanism and that maximizes an irradiation intensity of the reference light; wherein the optical component is configured to expand a beam diameter of the reference light to be larger at the second optical receiver than the receiving diameter of the second optical receiver.