PURPOSE: To detect the abnormal temperature, etc., in a house by providing a reflecting plate which reflects an electromagnetic or acoustic wave and a temperature sensing member which changes in shape with temperature and changes the direction of the reflecting plate.

CONSTITUTION: When the temperature sensing member 2 expands with temperature and the reflecting plate 1 on which an electromagnetic or acoustic wave ωis incident slants upward, the reflection direction of the electromagnetic or acoustic wave ω changes. Therefore, variation in temperature is detected from a change in the reflection direction of the electromagnetic or acoustic wave ω. Further, a rod 5 to be supported which is provided on the rear surface of the reflecting plate 1 and a support rod 4 which is provided on the front surface of a fitting plate 3 are coupled mutually by a shaft 6 to support the reflecting plate 1 rotatably, so the plate is supported more strongly than when the temperature sensing member 2 is fixed directly to the reflecting plate 1 and fitting plate 3. Consequently, the temperature variation is detected from the change in the reflection direction of the electromagnetic or acoustic wave.