To provide a small-sized atom interferometer.SOLUTION: An atom interferometer 500 comprises: an optical modulation device 510x including optical fibers 511x and 514x in which a first laser beam propagates and a frequency shifter 513x connected to the optical fibers 511x and 514x and for shifting the frequency of the first laser beam; an optical system 300 for forming a traveling light standing wave from the first laser beam from the optical modulation device 510x and a second laser beam facing the first laser beam from the optical modulation device 510x; and an interference system 200 in which an atomic beam 100a and three or more traveling light standing waves 200a, 200b and 200c interact.SELECTED DRAWING: Figure 3