Light-emitting diode controller 10 contains voltage source circuit 33 for feeding voltage to the anode of light-emitting diode 13, current source circuit 34 that selectively feeds current to the cathode of light-emitting diode 13, first voltage detector 36 that compares the cathode voltage of light-emitting diode 13, connected to current source circuit 34, to a first reference voltage, second voltage detector 37 that compares the cathode voltage to a second reference voltage lower than said first reference voltage, and voltage controllers 32, 35 that control the voltage value of the voltage fed from current source circuit 34. Here, voltage controllers 32, 35 control voltage source circuit 33 so that the voltage fed by current source circuit 34 is in the range between the first reference voltage and the second reference voltage.