A ceiling-mounted air conditioner comprising: a main body which has an open bottom so as to draw air thereinto through the open bottom; an intake panel which is disposed at the bottom of the main body and has an air intake in the middle, the air intake forming part of the open bottom of the main body; an outlet panel which is disposed at the bottom of the main body and includes a plurality of air outlets formed along the boundaries thereof and having heat-exchanged air ejected therefrom, a door panel which is lifted up and down below the main body and thus opens or shuts the open bottom of the main body; and a plurality of elevation devices which lift up or down the door panel, characterized in that each of the elevation devices includes: a plurality of moving elements, which are fixed onto the top surface of the door panel and are in engagement with the door panel so as to be able to lift up or down the door panel, a plurality of rotation elements, which are disposed in the main body and lift up or down the door panel by being placed in contact with the moving elements, a shaft, which is connected between the rotation elements, a shaft driving unit (231, 233), which is connected to one of the rotation elements and applies rotation force to the shaft so as for the shaft to be able to rotate, the rotation elements, the shaft and the shaft driving unit (231, 233) being installed on the intake panel, a shaft bracket, which is disposed on the intake panel, surrounds part of the circumferential surface of the shaft, and supports the shaft so as to be able to rotate, and a motor cover, which is disposed on the intake panel, surrounds the shaft driving unit (231, 233) and part of the circumferential surface of the shaft and supports the shaft so as to be able to rotate, and the shaft driving unit (230, 231, 233) being disposed near one of the rotation elements, and the shaft bracket is disposed near another one of the rotation elements, the intake panel further including a hook groove, and a first end portion of the shaft bracket being inserted into the hook groove. a main body which has an open bottom so as to draw air thereinto through the open bottom; an intake panel which is disposed at the bottom of the main body and has an air intake in the middle, the air intake forming part of the open bottom of the main body; an outlet panel which is disposed at the bottom of the main body and includes a plurality of air outlets formed along the boundaries thereof and having heat-exchanged air ejected therefrom, a door panel which is lifted up and down below the main body and thus opens or shuts the open bottom of the main body; and a plurality of elevation devices which lift up or down the door panel, characterized in that each of the elevation devices includes: a plurality of moving elements, which are fixed onto the top surface of the door panel and are in engagement with the door panel so as to be able to lift up or down the door panel, a plurality of rotation elements, which are disposed in the main body and lift up or down the door panel by being placed in contact with the moving elements, a shaft, which is connected between the rotation elements, a shaft driving unit (231, 233), which is connected to one of the rotation elements and applies rotation force to the shaft so as for the shaft to be able to rotate, the rotation elements, the shaft and the shaft driving unit (231, 233) being installed on the intake panel, a shaft bracket, which is disposed on the intake panel, surrounds part of the circumferential surface of the shaft, and supports the shaft so as to be able to rotate, and a motor cover, which is disposed on the intake panel, surrounds the shaft driving unit (231, 233) and part of the circumferential surface of the shaft and supports the shaft so as to be able to rotate, and the shaft driving unit (230, 231, 233) being disposed near one of the rotation elements, and the shaft bracket is disposed near another one of the rotation elements, the intake panel further including a hook groove, and a first end portion of the shaft bracket being inserted into the hook groove. a plurality of moving elements, which are fixed onto the top surface of the door panel and are in engagement with the door panel so as to be able to lift up or down the door panel, a plurality of rotation elements, which are disposed in the main body and lift up or down the door panel by being placed in contact with the moving elements, a shaft, which is connected between the rotation elements, a shaft driving unit (231, 233), which is connected to one of the rotation elements and applies rotation force to the shaft so as for the shaft to be able to rotate, the rotation elements, the shaft and the shaft driving unit (231, 233) being installed on the intake panel, a shaft bracket, which is disposed on the intake panel, surrounds part of the circumferential surface of the shaft, and supports the shaft so as to be able to rotate, and a motor cover, which is disposed on the intake panel, surrounds the shaft driving unit (231, 233) and part of the circumferential surface of the shaft and supports the shaft so as to be able to rotate, and the shaft driving unit (230, 231, 233) being disposed near one of the rotation elements, and the shaft bracket is disposed near another one of the rotation elements, the intake panel further including a hook groove, and a first end portion of the shaft bracket being inserted into the hook groove.