To make the constitution compact by measuring the pressure and a temperature of a plate having an electric fault by one unit in a wide range.

A light emitting diode 22 emits a pulse light and introduces the light into an optical fiber 23 via a half-mirror 24. A backward scattering light due to a propagation of the pulse light through the fiber 23 is guided to an avalanche photodiode 27 via the mirror 24. A light refractive index is changed corresponding to a pressure and a temperature at pressure element 25 and a temperature element 25 disposed at a predetermined interval in the fiber 23. And, an amount of the backward scattering light is changed as the index is changed. The scattering light is converted into an electric signal by the photodiode 27. The signal is then signal processed by a signal processor 28, thereby detecting pressure and temperature changes at positions where the elements 25, 26 disposed at predetermined positions in the fiber 23 are placed.