An optical interferometer includes: a light source that emits a coherent first beam and a second beam that has a frequency difference corresponding to the natural frequency of a target molecule; amplitude modulating means that modulates the amplitude of the second beam; splitting means that splits the first beam into a reference beam and a first applied beam; optical path length adjusting means that adjusts the optical path length of the reference beam; and detecting means that detects an interference pattern between the reference beam and the first beam (a signal beam) that has experienced a stimulated Raman loss or gain in accordance with the amplitude modulation as a result of the frequency difference resonating with the target molecule when the first applied beam and a second applied beam (the amplitude modulated second beam) have been applied to a measurement position of an object.