PURPOSE: To automatically regulate a blast amount without adding a control system when temperature in a device and an ambient temperature are changed by a method wherein a vane is formed with a plurality of vane pieces and a shape memory alloy through which the vane pieces are interconnected and the shape of which is changed when temperature exceeds a specified value.

CONSTITUTION: First and second connection pieces 7 and 8 are formed by a shape memory alloy and are restored to respective stored shapes at temperatures T1 and T2 (T1<T2). When an ambient temperature T is lower than T1 and T2, the connection pieces 7 and 8 are left in an original arcuate shape, and the shape of a vane 3 is curved. When the temperature T is T1≤T≤T2, the connection piece 7 is restored to a linear shape being a stored shape and therefore, small vanes 4 and 5 are arranged on a straight line, and a pitch is increased to increase an airflow. Further, when the temperature T is T2<T1, the connection piece 8 is brought into a stored linear shape, the vane 3 is linearly stretched and a pitch is increased to a higher value, and an airflow is further increased. When an ambient temperature is decreased as a result of cooling, the connection piece is restored to an original arcuate shape, and an airflow is decreased. This constitution performs blast in an optimum amount responding to temperature inside a device and temperature outside the device.