There is provided a laser gauge interferometer with high measurement precision, which uses laser beam interference, includes: a measurement interferometer which generates a measurement output corresponding to a displacement of a moving member; and a correction interferometer which generates a measurement output corresponding to a change in refractive index of air at a constant reference interval. An arithmetic processing device computes a measurement target displacement amount for which the influence of the change in refractive index of air is corrected. A correction laser beam from the correction interferometer passes through the measurement interferometer and thus travels on the same optical path as an optical path of a correction laser beam from the measurement interferometer to become interference light corresponding to the change in refractive index of air through which a measurement laser beam passes, and then enters the arithmetic processing device.