PURPOSE: To bend a blade to a side at a thin part as a center to reduce an apparent size of the blade and to facilitate assembling of the blade by forming the thin part at a center of the blade in a direction perpendicular to a rotary shaft in the blade supported between a pair of walls.

CONSTITUTION: A wind direction altering device comprises a plurality of blades 2 made of synthetic resin and aligned in parallel in a diffuser 1. Shafts 5, 6 are formed at one of a pair of walls 3, 4 and the blades 2 in the diffuser 1 and bearings 7, 8 to be engaged with the shafts 5, 6 are formed at the other. Thus, the blade 2 is rotatably disposed in the diffuser 1. With the above structure, a thin part 9 extended in a direction perpendicular to a rotary shaft O is formed at a center of the blade 2. When the blade 2 is assembled in the diffuser 1, the blade 2 is bent to a side at the thin part 9 as a center. Thus, an apparent size of the blade 2 in a direction of the shaft O is reduced to facilitate its assembling.