PURPOSE: To make thermal energy convertible to mechanical energy so efficiently and easily, by inserting a wire form memory alloy into a flexible pipe, and clamping the one end to the flexible pipe.

CONSTITUTION: A clamping device 2 is fitly clamped to one end of a flexible pipe 1 having flexibility, composed of synthetic resin, and a ferrule 3 to the other end of the flexible pipe 1, respectively, and an alloy insertion hole 3a is formed in a central part of the ferrule 3. And, one end of a form memory alloy 4 made of a wire Ti-Ni alloy, to which such a form that comes to an overall length L, inserted into the flexible pipe 1 passing through this alloy insertion hole 3a, is attached to the clamping device 2, while the other end of the form memory alloy 4 is drawn out to the outside of the flexible pipe 1. In addition, a tip fitting device 5 is clamped to and end of this form memory alloy 4 drawn out to the outside, and a compression coiled spring 6 giving a tensile force to the form memory alloy 4 is installed interposingly between the ferrule 3 and this tip fitting device 5.