PURPOSE: To have automatic alteration of the wind quantity and speed according to the change in temperature using a simple construction, by forming at least part of the construction from a bi-directional shape memory alloy so that any temp. change of the suction or exhaust gas causes corresponding alteration of the torsional angle.

CONSTITUTION: Vanes 2 installed on a boss 1 solidly are made of a shape memory alloy such as NiTi alloy, and the shape of each vane 2 is altered automatically as shown by the solid and dot-and-dash lines according to the temp. of the wind blowing against it so that its torsional angle is adjusted. The temp. when the shapes shall be altered is so arranged to be equal for all vanes 2, and the amount of torsional angle alteration and its direction also be equal for all vanes 2. This will provide alteration of the torsional angle, i.e. of wind quantity, according to the temp. change by a simple construction at a low cost without requiring equipment of any temp. sensor or voltage controller.