A PMOS transistor is inserted in a circuit connecting a power supply terminal of a power supply circuit and a battery terminal. When a control signal input terminal goes to a low level, it is decided that a PWM signal or an H control signal is input into the control signal input terminal. Then, transistors are turned on, and then the PMOS transistor is turned on to apply a battery voltage to the power supply circuit via a power supply terminal, whereby a supply of current to an LED is controlled by the control signal. When the control signal input terminal goes to a high level, it is decided that an L control signal is input as the control signal. Then, the transistors are turned off, and then the PMOS transistor is turned off to cut off a power supply to the power supply circuit from a battery, whereby a dark current can be prevented from flowing through the power supply circuit when the LED is turned off.