A headlight for a vehicle includes a metal halide lamp and a reflector having a focus and reflecting a light beam, emitted from the lamp, in a forward direction from the front of the vehicle. The lamp has a luminescent tube in which at least sodium is sealed, and positive and negative electrodes. The respective distal ends of the electrodes are located in the luminescent tube and spaced at a predetermined distance from each other. The lamp is positioned so that a straight line connecting the respective distal ends of the electrodes is horizontal and passes through the focus, and so as to meet the following requirement:0.ltoreq.L0/L1.ltoreq.0.4,where L0 is the distance between the focus and the distal end of the negative electrode, and L1 is the distance between the distal ends of the electrodes.