PURPOSE: To amplify/convert physical quantity into the axial direction displacement of cylindrical surface by restricting deformation of curvature change element that is formed in elongated spiral shape and its curvature changes according to physical quantity such as temperature and electrical current from outside within cylindrical surface by a ristricting mechanism.

CONSTITUTION: In three elongated bimetal elements 1A-1C formed in spiral, a restriction mechanism 2 that restricts their deformation within cylindrical surface is provided. The mechanism 2 consists of multiple hard rings 2A-2E, where a connection pin 2a provided at specified intervals in the axial direction Z-Z' of the spiral on the peripheral side are rotation-connected to the corresponding parts of corresponding elements 1A-1C, and a guide rod 2F that penetrates through a center hole 2c of a traverse arm 2b in the radius direction of rings 2A-2D. The rod 2F is fixed to the arm 2b of the ring 2E jointed to a movable end of the elements 1A-1C, to work as an output rod. Since the rod 2F significantly changes according to curvature changes of elements 1A-1C, axial direction displacement obtained by amplifying temperature changes can be taken out.