In conduction of light emitting diodes LEDs 1 to 4, a switching signal 101 is converted into a voltage V2 or 0V through a signal converter 26 in accordance with a logic level thereof. The voltage obtained by the conversion is compared with a voltage V1 on both ends of a resistor R1 through an operational amplifier 20 to open/close an output loop by an NMOS transistor 22, a current If of the light emitting diodes LEDs 1 to 4 is limited to a current If1 so as not to exceed a maximum current, and a current defined with an ON duty of the switching signal 101 is caused to flow as a mean current to the light emitting diodes LEDs 1 to 4 to inhibit an overshoot current from flowing to the light emitting diodes LEDs 1 to 4 while the output loop is closed.