This atomic clock comprises means for applying two mutually perpendicular oscillating magnetic fields (9, 10), governed by a control device (5) that makes them apply a static or nearly static magnetic field for compensating the ambient magnetic field in order to cancel sub-level energy variations of the matter, which disrupt the frequency of the returned photons and the reference provided by the clock. Traditional magnetic shielding may be omitted. Said device can also operate as a magnetometer.