Abstract: Disclosed is an interferometer comprising a light source, a reflective element, and a photodetector. The light source is configured to emit a light beam, and an angle is formed by inclusion between a direction to which the light beam travels and the reflective element, the photodetector is configured to be substantially perpendicular to the reflective element. The light beam is halved into a first light beam propagating by the included angle, and a second light beam reflected off the reflective element, the first light beam and the second light beam interfere each other to form an interferogram on the photodetector, which detects the interferogram. By benefit of above, the interferometer does not need to reposition its parts in order to make adjustment to interferogram, thereby simplifying optical element setup and minimizing physical volume of the interferomger. Also disclosed is a spectrometer including the same interferometer and a Fourier-transform-capable analyzer.