Abstract: A louver is pivotally secured to a body in an air passage formed between side walls for altering the diffusing direction of diffused air. A device for changing the angle of the louver comprises a shape memory alloy spring for urging rotary force to the louver in one direction by fittings mounted at the side walls of the body and the louver, as required, and a bias spring for urging rotary force reverse to the louver in such a manner that the shape memory alloy spring and the bias spring are balanced in the air passage. The shape memory alloy spring is deformed by the bias spring when chilled air is fed to the passage to tiltably incline the louver. The shape memory alloy spring returns to a memorized position when warm air is fed to the passage to rotate the louver to a position aligned with the passage against the bias spring. Thus, the louver can be automatically controlled by sensing the temperature of the diffused air by the shape memory alloy spring and the bias spring.