PURPOSE: To perform accurate detection by fixing a marker plate atop of a linear shape memory element material whose intermediate part flexes and/or rotates under specific temperature, and fitting the base part to a detection position of a member to be detected.

CONSTITUTION: The discoid marker plate 2 is fixed to the tip part of the linear shape memory material 1, whose base end part is wound to form a loop part 3. In this case, the surfaces of the front surface part and rear surface part of the marker plate 2 are colored in, for example, red or yellow to detect an abnormal overheat. The loop part 3 formed at the base end part of the shape memory element 1 is a fitting part for attachment to the member to be detected. Consequently, the temperature deformation of the shape memory element is accurate, so its detection is performed accurately and the reliability is improved.