In a process in which a control signal having a low level is output from an ON/OFF control circuit to series regulators connected to LEDs serving as lighting targets to turn ON the LEDs in accordance with digital communication information, the ON/OFF control circuit calculates a specified current value to be supplied to the LEDs serving as the lighting targets and compares the specified current value with a detected current value which is detected by a current detecting circuit, and outputs a stop signal to a control circuit on the assumption that a current flows without the series regulators with grounding generated on a cathode side of any of LEDs when the detected current value is greater than the specified current value. When the control circuit turns OFF an NMOS transistor in response to the stop signal, an operation of a switching regulator is stopped.