An air duct includes a main body and a panel. The main body includes a top wall defining a depressed portion. A front wall of the depressed portion defines an inlet. A rear wall of the depressed portion defines two outlets. The top wall forms two fixing portions at the front side of the top wall. A pole is mounted to the rear side of the top wall, between the outlets. A first end of the panel is rotatably connected to the pole; a second end of the board opposite to the first end is operable to be selectively mounted to one of the fixing portions.