A position measuring system includes a laser interferometer, and a wavelength detection unit detecting the wavelength change of a laser beam. A phase compensation unit compensates for the wavelength change detected by the wavelength detection unit based on the phase difference of aerial vibration between the wavelength detection unit and the optical path of the laser interferometer, which is determined based on the difference in length between a first path of the aerial vibration from the aerial vibration source of an air conditioner to the wavelength detection unit and a second path of the aerial vibration from the aerial vibration source to the optical path of the laser interferometer. A position measuring unit compensates for a measurement value obtained by the laser interferometer on the basis of the compensated wavelength change. In the position measuring system, the first path is designed to be shorter than the second path.