A head-up display (HUD) comprises a detection unit, a picture generating unit and a control unit. The detection unit detects a position of an object and generates a detection signal indicated the position of the object. The picture generating unit comprises a screen and an optical unit. The screen displays a visual image. The optical unit projects the visual image onto the screen. The control unit is coupled to the detection unit and the picture generating unit, controlling the screen to facing toward the object in response to the detection signal.