The diode driver circuit comprises switching means (2, 3) responsive to an input signal, a diode means (13) for modulation or switching, a low impedance circuit means (9) connected to the switching means (2, 3) and the diode means (13) for feeding a reverse voltage to the diode means (13) in response to the output of the switching means (2, 3), and a constant current circuit means (11) connected to the diode means (13) for supplying a current in the forward direction to the diode means (13). The constant current circuit means (11) includes means for supplying an excess current for only a short period from the time the diode means is biassed from the reverse to the forward. This high-speed diode driver circuit has a lower power consumption and can be readily reduced in size (Figure 1).