The temperature measuring device of the present invention comprises: a light source for outputting light; an optical fiber to which light outputted by the light source is inputted and from which Brillouin scattered light is outputted; a detection unit for detecting a spectrum of the Brillouin scattered light; a judgment unit for judging whether or not a frequency shift of the spectrum of the Brillouin scattered light detected by the detection unit belongs to a specific region in which the rate of change of the frequency shift with respect to the temperature of the optical fiber is smaller than a predetermined value; and an analysis unit for, when the judgment unit judges that the frequency shift does not belong to the specific region, analyzing the temperature in use of the frequency shift, and for, when the judgment unit judges that the frequency shift belongs to the specific region, not performing analysis, or analyzing the temperature in use of at least the linewidth of the spectrum of the Brillouin scattered light detected by the detection means.