There is provided a distortion measuring device including a Brillouin scattered light spectrum recording unit which records a spectrum of Brillouin scattered light generated in an optical fiber as a result of supplying incident light, a peak frequency approximating unit which acquires an approximated peak frequency at which the recorded spectrum takes a maximal value, a peak frequency deriving unit which derives a peak frequency at which the spectrum takes the maximal value within a range of a frequency determined based on a magnitude of the spectrum at the approximated peak frequency, amid a distortion deriving unit which derives distortion of the optical fiber based on the derived peak frequency.