A display unit includes a housing having a front end portion, upper and lower walls, and two opposite side walls, and formed with a rib that protrudes from one of the upper and lower walls and that extends between the side walls in a transverse direction relative to the side walls, and a retaining groove that is indented from the other of the upper and lower walls, and that extends between the side walls in the transverse direction. When two of the display units are stacked one above the other, the rib on one of the display units is fitted into the retaining groove in the other of the display units. A screen is mounted on the front end portion of the housing. An image projecting device is mounted in the housing for projecting images onto the screen.