The present invention relates to an air conditioner for a vehicle, which includes an air-conditioning case (200), and at least one door (100) mounted to be opened and closed at a predetermined position, wherein the door (100) is formed integrally with an arm pivot (140), and the arm pivot (140) includes a pin part, and ribs formed integrally with both sides of the pin part to reinforce rigidity of the pin part and offset noise. The air conditioner further includes distortion preventing parts formed on a rotary shaft to be dented and to be crossed to each other, thereby reducing a transformation rate of the door and securing accuracy of the pin part.