Disclosed herein is an air conditioning diffuser having a function of changing an air supply direction. The diffuser of the present invention includes a frame (10) and a temperature sensing cylinder (20), which is coupled to the frame (10). A wax (21) is charged in the cylinder (20), and a piston rod (22) is provided in the cylinder (20). The diffuser further includes a blade support body (50), coupled to the cylinder (20), a pushing member (23), coupled to the piston rod in the blade support body, and a vertical movable member (40), which is provided in the blade support body (40) and is pushed downwards by the pushing member (23) when the wax is expanded. The diffuser further includes air guide blade assemblies (30), which are supported by the blade support body (50) and are coupled to the vertical movable member (40) so that, when the vertical movable member is moved upwards or downwards, blades (35) are rotated. An elastic member is provided under the vertical movable member (40).