A laser oscillation frequency stabilizer including a laser light source portion having a laser light source whose oscillation frequency can be controlled and configured to emit a laser beam. The frequency stabilizer includes a polarized beam splitter configured to split a laser beam from the laser light source portion into laser beams having linearly polarized components. The frequency stabilizer includes a quarter wavelength plate converts the laser beams, split by the polarized beam splitters, into circularly polarized laser beams. Further, an absorption cell sealed with gaseous atoms or molecules having a certain absorption spectrum is disposed in an optical path of the circularly polarized laser beams, and has a uniform magnetic field applied thereto. A half mirror reflects partially each of the circularly polarized laser beams back through the absorption cell. A control portion controllably locks the oscillation frequency of the laser light source in accordance with transmitted light reception levels of laser light having passed in opposite directions through the absorption cell