The frequency of a three-longitudinal mode He–Ne laser was stabilized by the method of detecting the secondary beat frequency between modes. The stabilized laser has been efficiently used as a laser source for a distance meter. In distance measurement, two intermode beat frequencies (875 MHz, 145 kHz) were, respectively, used as a modulation frequency instead of an optical modulator. The resolution of the distance meter was higher than 20 μm. The total uncertainty was within 20 μm by correction of errors except for the uncertainty of the refractive index of the air.